Mitigating Congestion

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 is taking place at major highways serving 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 random groups. The outcome is a lower disruption on highway traffic flows through better merging.

·         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 hourly to reflect changes in circulation patterns. Trucks can be allowed to pass traffic lights through delayed signals, which 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. Such strategies, however, go against market principles.

·         Sharing vehicles. Concerns two issues. The first is 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 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 the next section about urban transit challenges).

·         Non-motorized transportation. Since most urban trips are over short distances, non-motorized modes, particularly walking and cycling, have an important role 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 despite 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.