Table of Contents
Author: Dr. Jean-Paul Rodrigue
The most important transport challenges take place when urban transport systems, for a variety of reasons, cannot satisfy the requirements of urban mobility.
Cities are locations having a high level of accumulation and concentration of economic activities. They are complex spatial structures supported by complex infrastructure, including transport systems. The larger a city, the greater its complexity and the potential for disruptions, particularly when this complexity is not effectively managed. Urban productivity is highly dependent on the efficiency of its transport system to move labor, consumers, and freight between multiple origins and destinations. Additionally, transport terminals such as ports, airports, and railyards are located within urban areas, contributing to a specific array of challenges. Some are ancient, like congestion (which plagued cities such as Rome), while others are new like urban freight distribution or environmental impacts.
a. Traffic congestion and parking difficulties
Congestion is one of the most prevalent transport challenges in large urban agglomerations, usually above a threshold of about 1 million inhabitants. By the 21st century, drivers are three times more likely to be affected by congestion than in the latter part of the 20th century. Congestion is particularly linked with motorization and the diffusion of the automobile, which has increased the demand for transport infrastructures. However, the supply of infrastructures has often not been able to keep up with the growth of mobility. Since vehicles spend the majority of the time parked, motorization has expanded the demand for parking space, which has created space consumption problems particularly in central areas; the spatial imprint of parked vehicles is significant.
Congestion and parking are also interrelated since street parking consumes transport capacity, removing one or two lanes for circulation along urban roads. Further, looking for a parking space (called “cruising”) creates additional delays and impairs local circulation. In central areas of large cities cruising may account for more than 10% of the local circulation as drivers can spend up to 20 minutes looking for a parking spot. This practice is often judged more economically effective than using a paying off-street parking facility as the time spent looking for a free (or low cost) parking space is compensated by the monetary savings. Also, many delivery vehicles will simply double-park at the closest possible spot to unload their cargo.
Identifying the true cause of congestion is a strategic issue for urban planning since congestion is commonly the outcome of specific circumstances such as the lack of parking or poorly synchronized traffic signals.
b. Longer commuting
On par with congestion, people are spending an increasing amount of time commuting between their residence and workplace. An important factor behind this trend is related to residential affordability as housing located further away from central areas (where most of the employment remains) is more affordable. Therefore, commuters are exchanging commuting time for housing affordability. However, long commuting is linked with several social problems, such as isolation (less time spent with family or friends), as well as poorer health (obesity).
c. Public transport inadequacy
Many public transit systems, or parts of them, are either over or underused since the demand for public transit is subject to periods of peaks and troughs. During peak hours, crowdedness creates discomfort for users as the system copes with a temporary surge in demand. Low ridership makes many services financially unsustainable, particularly in suburban areas. In spite of significant subsidies and cross-financing (e.g. tolls), almost every public transit system cannot generate sufficient income to cover its operating and capital costs. While in the past deficits were deemed acceptable because of the essential service public transit was providing for urban mobility, its financial burden is increasingly controversial.
d. Difficulties for non-motorized transport
These difficulties are either the outcome of intense traffic, where the mobility of pedestrians, bicycles and other non-motorized vehicles is impaired, but also because of a blatant lack of consideration for pedestrians and bicycles in the physical design of infrastructures and facilities. On the opposite side, the setting of bicycle paths takes capacity away from roadways as well as parking space. A negative outcome would be to allocate more space for non-motorized transport than the actual mobility demand, which would exacerbate congestion.
e. Loss of public space
Most roads are publicly owned and free of access. Increased traffic has adverse impacts on public activities which once crowded the streets such as markets, agoras, parades and processions, games, and community interactions. These have gradually disappeared to be replaced by automobiles. In many cases, these activities have shifted to shopping malls while in other cases, they have been abandoned altogether. Traffic flows influence the life and interactions of residents and their usage of street space. More traffic impedes social interactions and street activities. People tend to walk and cycle less when traffic is high.
f. High infrastructure maintenance costs
Cities facing the aging of their transport infrastructure have to assume growing maintenance costs as well as pressures to upgrade to more modern infrastructure. In addition to the involved costs, maintenance and repair activities create circulation disruptions. Delayed maintenance is rather common since it conveys the benefit of keeping current costs low, but at the expense of higher future costs and on some occasion the risk of infrastructure failure. The more extensive the road and highway network, the higher the maintenance cost and its financial burden.
g. Environmental impacts and energy consumption
Pollution, including noise, generated by circulation has become an impediment to the quality of life and even the health of urban populations. Further, energy consumption by urban transportation has dramatically increased and so the dependency on petroleum. These considerations are increasingly linked with peak mobility expectations where high energy prices incite a shift towards more efficient and sustainable forms of urban transportation, namely public transit.
h. Accidents and safety
Growing traffic in urban areas is linked with a growing number of accidents and fatalities, especially in developing economies. Accidents account for a significant share of recurring delays. As traffic increases, people feel less safe to use the streets. The diffusion of information technologies leads to paradoxical outcomes. While users have access to reliable location and navigation information, portable devices create distractions linked with a rise of accidents for drivers and pedestrians alike.
i. Land footprint
The territorial footprint of transportation is significant, particularly for the automobile. Between 30 and 60% of a metropolitan area may be devoted to transportation, an outcome of the over-reliance on road transportation. Yet, this footprint also underlines the strategic importance of transportation in the economic and social welfare of cities.
j. Freight distribution
Globalization and the materialization of the economy have resulted in growing quantities of freight moving within cities. As freight traffic commonly shares infrastructures with the circulation of passengers, the mobility of freight in urban areas has become increasingly problematic. The growth of e-commerce and home parcel deliveries have created additional pressures in the urban mobility of freight. City logistics strategies can be established to mitigate the variety of challenges faced by urban freight distribution.
Many dimensions to the urban transport challenge are linked with the dominance of the automobile.
Automobile use is obviously related to a variety of advantages such as on-demand mobility, comfort, status, speed, and convenience. These advantages jointly illustrate why automobile ownership continues to grow worldwide, especially in urban areas and developing economies. When given the choice and the opportunity, most individuals will prefer using an automobile. Several factors influence the growth of the total vehicle fleet, such as sustained economic growth (increase in income and quality of life), complex individual urban movement patterns (many households have more than one automobile), more leisure time and suburbanization. Therefore, rising automobile mobility can be perceived as a positive consequence of economic development. The automotive sector is a factor of economic growth and job creation with several economies actively promoting it.
The acute growth in the total number of vehicles also gives rise to congestion at peak traffic hours on major thoroughfares, in business districts and often throughout the metropolitan area. Cities are important generators and attractors of mobility, which is associated with a set of geographical paradoxes that are self-reinforcing. For instance, economic specialization leads to additional transport demands while agglomeration leads to congestion. Over time, a state of automobile dependency has emerged which results in a declining role of other modes, thereby limiting alternatives to urban mobility through path dependency. A city can become ‘locked in’ into planning decisions that reinforce the use of the automobile. In addition to the factors contributing to the growth of driving, two major factors contributing to automobile dependency are:
- Underpricing and consumer choices. Most roads and highways are subsidized as they are considered a public good. Consequently, drivers do not bear the full cost of automobile use, such as parking. Like the “Tragedy of the Commons”, when a resource is free of access (road), it tends to be overused and abused (congestion). This is also reflected in consumer choice, where automobile ownership is a symbol of status, freedom, and prestige, especially in developing economies. Single home ownership also reinforces automobile dependency and if this ownership is favored through various subsidies.
- Planning and investment practices. Planning and the ensuing allocation of public funds aim towards improving road and parking facilities in an ongoing attempt to avoid congestion. Other transportation alternatives tend to be disregarded. In many cases, zoning regulations impose minimum standards of road and parking services, such as the number of parking spaces per square meter of built surface, and de facto impose a regulated automobile dependency.
There are several levels of automobile dependency, ranging from low to acute, with their corresponding land use patterns and alternatives to mobility. Among the most relevant indicators of automobile dependency is the level of vehicle ownership, per capita motor vehicle mileage and the proportion of total commuting trips made using an automobile. A situation of high automobile dependency is reached when more than three-quarters of commuting trips are done using the automobile. For the United States, this proportion has remained around 88% over recent decades.
Automobile dependency is also served by a cultural and commercial system promoting the automobile as a symbol of status and personal freedom, namely through intense advertising and enticements to purchase new automobiles. Not surprisingly, many developing economies perceive motorization as a condition for development. Even if the term automobile dependency is often negatively perceived and favored by market distortions such as the provision of roads, its outcome reflects the choice of individuals who see the automobile more as an advantage than an inconvenience. This can lead to a paradoxical situation where planners try to counterbalance the preference of automobile ownership supported by the bulk of the population.
The second half of the 20th century saw the adaptation of many cities to support automobile circulation. Motorized transportation was seen as a symbol of modernity and development. Highways and parking lots were constructed and streets were enlarged, often disrupting the existing urban environment with the creation of motorized cities. However, from the 1980s, motorization started to be seen more negatively and several cities implemented policies to limit automobile circulation, at least in specific areas, by a set of strategies including:
- Dissuasion. Although automobile circulation is permitted, it is impeded by regulations and physical planning. For instance, parking space can be severely limited or subject to pricing and speed bumps placed to force speed reduction.
- Prohibition of downtown circulation. During most of the day the downtown area is closed to automobile circulation, but deliveries are permitted during the night. Such strategies are often undertaken to protect the character and the physical infrastructures of a historical city. They do, however, like most policies, have unintended consequences. If mobility is restrained in certain locations or during certain time periods, people will simply go elsewhere (longer movements) or defer their mobility for another time (more movements).
- Tolls. Imposing tolls for parking and entry (congestion pricing) to some parts of the city has been a strategy being considered seriously in many areas as it confers the potential advantage of congestion mitigation and revenue generation. Most evidence underlines however that drivers are willing to bear additional toll costs for the convenience of using a car, especially for commuting since it is linked with their main source of income.
Tentative solutions have been put forth such as transport planning measures (synchronized traffic lights, regulated parking), limited vehicle traffic in selected areas, the promotion of bicycle paths and public transit. In Mexico City, vehicle use is allowed on specific weekdays according to license plate numbers, implying that a vehicle will be prevented to circulate at least one weekday. Affluent families have solved this issue by purchasing a second vehicle, thus worsening the existing situation. Singapore is the only country in the world that has successfully controlled the amount and growth rate of its vehicle fleet by imposing a heavy tax burden and purchasing permits on automobile owners. Since Singapore is of small size and has an extensive public transit system, this restriction does not impair much mobility. However, such a command-based approach is unlikely to be possible in other contexts.
There is a growing body of evidence underlining that a peak level of car mobility is unfolding, at least in developed economies. Higher energy prices, congestion, less economic prospects and the general aging of the population are all countervailing forces to car dependency. For instance, from 2006 the number of vehicle-miles traveled in the United States peaked for almost a decade, a process associated with higher energy prices and an economic recession. There are many alternatives to automobile dependency such as intermodality (combining the advantages of individual and collective transport), carpooling or non-motorized transportation (walking and cycling). These alternatives can only be partially implemented as the automobile remains on the short and medium terms the prime choice for providing urban mobility. A significant potential change remains the development of mobile car-sharing applications enabling better utilization of vehicle assets. Although this would not reduce the level of automobile dependency, it can offer enough flexibility for some users not to require the ownership of an automobile.
Congestion occurs when transport demand exceeds transport supply at a specific point in time and in a specific section of the transport system. Under such circumstances, each vehicle impairs the mobility of others.
Congestion can be perceived as an unavoidable consequence of the usage of scarce transport resources, particularly if they are not priced. The last decades have seen the extension of roads in urban areas, most of them free of access. Those infrastructures were designed for speed and high capacity, but the growth of urban circulation occurred at a rate higher than often expected. Investments came from diverse levels of government with a view to providing accessibility to cities and regions. There were strong incentives for the expansion of road transportation by providing high levels of transport supply. This has created a vicious circle of congestion which supports the construction of additional road capacity and automobile dependency. Urban congestion mainly concerns two domains of circulation, often sharing the same infrastructures:
- Passengers. In many regions of the world, incomes have significantly increased; one automobile per household or more is becoming common. Access to an automobile conveys flexibility in terms of the choice of origin, destination and travel time. The automobile is favored at the expense of other modes for most trips, including commuting. For instance, automobiles account for the bulk of commuting trips in the United States. The majority of automobile-related congestion is the outcome of time preferences in the usage of vehicles (during commuting hours) as well as a substantial amount of space required to park vehicles. About 95% of the time an automobile is idle.
- Freight. Several industries have shifted their transport needs to trucking, thereby increasing the usage of road infrastructure. Since cities are the main destinations for freight flows (either for consumption or for transfer to other locations) trucking adds to further congestion in urban areas. The “last mile” problem remains particularly prevalent for freight distribution in urban areas. Congestion is commonly linked with a drop in the frequency of deliveries tying additional capacity to ensure a similar level of service. The growth of home deliveries due to e-commerce has placed additional pressures, particularly in higher density areas, on congestion in part because of more frequent parking.
It is important to underline that congestion in urban areas is dominantly caused by commuting patterns and little by truck movements. On average, infrastructure provision was not able to keep up with the growth in the number of vehicles, even more with the total number of vehicles-km. During infrastructure improvement and construction, capacity impairment (fewer available lanes, closed sections, etc.) favors congestion. Important travel delays occur when the capacity limit is reached or exceeded, which is the case of almost all metropolitan areas. In the largest cities such as London, road traffic is slower than it was 100 years ago. Marginal delays are thus increasing and driving speed becomes problematic as the level of population density increases. Once a population threshold of about 1 million is reached, cities start to experience recurring congestion problems. This observation must be nuanced by numerous factors related to the urban setting, modal preferences (share of public transit) and the quality of existing urban transport infrastructures.
Large cities have become congested most of the day, and congestion was getting more acute in the 1990s and 2000s and then leveled off in many cases. For instance, average car travel speeds have substantially declined in China, with many cities experiencing an average driving speed of less than 20 km/hr with car density exceeding 200 cars per km of road, a figure comparable to many developed economies. Another important consideration concerns parking, which consumes large amounts of space and provides a limited economic benefit if not monetized. In automobile-dependent cities, this can be very constraining as each land use has to provide an amount of parking space proportional to their level of activity. Parking has become a land use that greatly inflates the demand for urban land.
Urban mobility also reveals congestion patterns. Daily trips can be either mandatory (workplace-home) or voluntary (shopping, leisure, visits). The former is often performed within fixed schedules while the latter complies with variable and discretionary schedules. Correspondingly, congestion comes in two major forms:
- Recurrent congestion. The consequence of factors that cause regular demand surges on the transportation system, such as commuting, shopping or weekend trips. However, even recurrent congestion can have unforeseen impacts in terms of its duration and severity. Mandatory trips are mainly responsible for the peaks in circulation flows, implying that about half the congestion in urban areas is recurring at specific times of the day and on specific segments of the transport system.
- Non-recurrent congestion. The other half of congestion is caused by random events such as accidents and unusual weather conditions (rain, snowstorms, etc.), which are unexpected and unplanned. Non-recurrent congestion is linked to the presence and effectiveness of incident response strategies. As far as accidents are concerned, their randomness is influenced by the level of traffic as the higher the traffic on specific road segments the higher the probability of accidents.
Behavioral and response time effects are also important as in a system running close to capacity, simply breaking suddenly may trigger what can be known as a backward traveling wave. It implies that as vehicles are forced to stop, the bottleneck moves up the location it initially took place at, often leaving drivers puzzled about its cause. The spatial convergence of traffic causes a surcharge on transport infrastructures up to the point where congestion can lead to the total immobilization of traffic. Not only does the massive use of the automobile have an impact on traffic circulation and congestion, but it also leads to the decline in public transit efficiency when both are sharing the same road infrastructures.
In some areas, the automobile is the only mode for which adequate transportation infrastructures are provided. This implies less capacity for using alternative modes such as transit, walking, and cycling. At some levels of density, no public infrastructure investment can be justified in terms of economic returns. Longer commuting trips in terms of average travel time, the result of fragmented land uses and congestion levels are a significant trend. A convergence of traffic at major highways that serve vast low-density areas with high levels of automobile ownership and low levels of automobile occupancy. The result is energy (fuel) wasted during congestion (additional time) and supplementary commuting distances. In automobile-dependent cities, a few measures can help alleviate congestion to some extent:
- Ramp metering. Controlling access to a congested highway by letting automobiles in one at a time instead of in groups. The outcome is a lower disruption on highway traffic flows.
- Traffic signal synchronization. Tuning the traffic signals to the time and direction of traffic flows. This is particularly effective if the signals can be adjusted on an hourly basis to reflect changes in commuting patterns. Trucks can be allowed to pass traffic lights through delayed signals. This reduces the risk of accidents through sudden collision with a car breaking at a yellow light. Therefore, trucks are less likely to be the first vehicle at a red light, which increases capacity because trucks have lower acceleration.
- Incident management. Making sure that vehicles involved in accidents or mechanical failures are removed as quickly as possible from the road. Since accidents account for 20 to 30% of all the causes of congestion, this strategy is particularly important.
- Car ownership restrictions. Several cities and countries (e.g. Singapore) have quotas in the number of license plates that can be issued or require high licensing fees. To purchase a vehicle an individual thus must first secure a license through an auction.
- Sharing vehicles. Concerns two issues. The first is an individual providing ridership to people (often co-workers) having a similar origin, destination and commuting time. Two or more vehicle trips can thus be combined into one, which is commonly referred to as carpooling. The second involves a pool of vehicles (mostly cars, but also bicycles) that can be leased or shared for a short duration when mobility is required. Adequate measures must be taken so that supply and demand are effectively matched with information technologies providing effective support.
- HOV lanes. High Occupancy Vehicle (HOV) lanes ensure that vehicles with two or more passengers (buses, taxis, vans, carpool, etc.) have exclusive access to a less congested lane, particularly during peak hours.
- Congestion pricing. A variety of measures aimed at imposing charges on specific segments or regions of the transport system, mainly as a toll. The charges can also vary during the day to reflect congestion levels so that drivers are incited to consider other time periods or other modes.
- Parking management. Removing parking or free parking spaces can be an effective dissuasion tool since it reduces cruising and enables those willing to pay to access an area (e.g. for a short shopping stop). Parking spaces should be treated as a scarce asset subject to a price structure reflecting the willingness to pay. Further, planning regulations provide an indirect subsidy to parking by enforcing minimum parking space requirements based upon the type and the density of the land use.
- Public transit. Offering alternatives to driving that can significantly improve efficiency, notably if it circulates on its own infrastructure (subway, light rail, buses on reserved lanes, etc.) and is well integrated within a city’s development plans. However, public transit has its own set of issues (see next section).
- Non-motorized transportation. Since the great majority of urban trips are over short distances, non-motorized modes, particularly walking and cycling, have an important role to play in supporting urban mobility. The provision of adequate infrastructure, such as sidewalks, is often a low priority as non-motorized transportation is often perceived as not modern in spite of the important role it needs to assume in urban areas.
All these measures only partially address the issue of congestion, as they alleviate, but do not solve the problem. Fundamentally, congestion remains the sign of economic success, but a failure at reconciling rising mobility demands and acute supply constraints.
As cities continue to become more dispersed, the cost of building and operating public transportation systems increases. For instance, as of 2015 about 201 urban agglomerations had a subway system, the great majority of them being in developed economies. Furthermore, dispersed residential patterns characteristic of automobile-dependent cities make public transportation systems less convenient to support urban mobility. Additional investments in public transit often do not result in significant additional ridership. Unplanned and uncoordinated land development has led to the rapid expansion of the urban periphery. Residents, by selecting housing in outlying areas, restrict their potential access to public transportation. Over-investment (when investments do not appear to imply significant benefits) and under-investment (when there is a substantial unmet demand) in public transit are both complex challenges.
Urban transit is often perceived as the most efficient transportation mode for urban areas, notably large cities. However, surveys reveal a stagnation of public transit systems, especially in North America, where ridership levels have barely changed in the last 30 years. The economic relevance of public transit is being questioned. Most urban transit developments had little, if any, impacts to alleviate congestion in spite of mounting costs and heavy subsidies. This paradox is partially explained by the spatial structure of contemporary cities which are oriented along servicing the needs of the individual, not necessarily the needs of the society. Thus, the automobile remains the preferred mode of urban transportation.
In addition, public transit is publicly owned, implying that it is a politically motivated service that provides limited economic returns. Even in transit-oriented cities, transit systems depend massively on government subsidies. Little or no competition within the public transit system is permitted as wages and fares are regulated, undermining any price adjustments to changes in ridership. Thus, public transit often serves the purpose of a social function (public service) as it provides accessibility and social equity, but with limited relationships with economic activities. Among the most difficult challenges facing urban transit are:
- Decentralization. Public transit systems are not designed to service low density and scattered urban areas that are dominating the urban landscape. The greater the decentralization of urban activities, the more difficult and expensive it becomes to serve urban areas with public transit. Additionally, decentralization promotes long-distance trips on transit systems causing higher operating costs and revenue issues for flat fare transit systems.
- Fixity. The infrastructures of several public transit systems, notably rail and subway systems are fixed, while cities are dynamical entities, even if the pace of change can take decades. This implies that travel patterns tend to change and that a transit system built for servicing a specific pattern may eventually face “spatial obsolescence”; the pattern it was designed to serve no longer exists.
- Connectivity. Public transit systems are often independent from other modes and terminals. It is consequently difficult to transfer passengers from one system to the other. This leads to a paradox between the preference of riders to have direct connections and the need to provide a cost-efficient service network that involves transfers.
- Automobile competition. In view of cheap and ubiquitous road transport systems, public transit faced strong competition and lost ridership in relative terms and in some cases in absolute terms. The higher the level of automobile dependency, the more inappropriate the public transit level of service. The public service being offered is simply outpaced by the convenience of the automobile.
- Construction and maintenance costs. Public transit systems, particularly heavy rail, are capital intensive to build, operate and maintain. Cost varies depending on local conditions such as density and regulations, but average construction costs are around $300 million per km. There are however exceptions where cost overruns can be substantial because of capture by special interest groups such as labor unions, construction companies, and consulting firms. When there is inefficient regulatory oversight, these actors will converge to extract as much rent as possible from public transit capital improvements. The world’s highest subway construction costs are in New York. For instance, the Second Avenue subway extension in Manhattan, completed in 2015, was done at a cost of $1.7 billion per km, five to seven times the average in comparable cities such as Paris or London. This project employed four times more labor with construction costs 50% higher.
- Fare structures. Historically, most public transit systems have abandoned a distance-based fare structure for a simpler flat fare system. This had the unintended consequence of discouraging short trips for which most transit systems are well suited for and encouraging longer trips that tend to be costlier per user than the fares they generate. Information systems offer the possibility for transit systems to move back to a more equitable distance-based fare structure, particularly with the usage of smartcards that enable to charge according to the point of entry and exit within the public transit system.
- Legacy costs. Most public transit systems employ unionized labor that have consistently used strikes (or the threat of a strike) and the acute disruptions they create as leverage to negotiate favorable contracts, including health and retirement benefits. Since public transit is subsidized these costs were not well reflected in the fare systems. In many transit systems, additional subsidies went into compensation or to cover past debt, and not necessarily into performance improvements or additional infrastructure. As most governments are facing stringent budgetary constraints because of social welfare commitments, public transit agencies are being forced to reassess their budgets through an unpopular mix of higher fares, deferred maintenance and the breaking of labor contracts.
- Self-driving vehicles. Developments in information technologies let anticipate in the coming years the availability of self-driving vehicles. Such a development would entail point to point services by on-demand vehicles and a much better utilization level of such assets. This system could compete directly with transit systems due to its convenience, comfort and likely affordability.
Public transit systems are therefore challenged to remain relevant to urban mobility as well as to increase its market share. The rise in petroleum prices since 2006 has increased the cost of vehicle ownership and operation, but it remains affordable. A younger generation is perceiving the automobile as a less attractive proposition than the prior generations and is more willing to use public transit and live in higher density areas. Electronic fare systems are also making the utilization of public transit more convenient. A recent trend concerns the usage of incentives, such as point systems (e.g. air miles with purchase of a monthly pass) to further promote the use of public transit and to influence consumer behavior. Yet, evidence underlines that the inflation adjusted cost of using public transit is increasing, implying that the cost advantage of public transit over the automobile is not changing in a significant manner. If self-driving vehicles become a possibility, many highly subsidized transit systems may have limited competitive advantage. Under such circumstances, the fate of many surface public transit systems will be in question.