Traffic management strategies aim to improve traffic conditions using techniques from traffic engineering and control, including access restrictions, lane management, and traffic control.
Access and Vehicle-Related Restrictions
These measures use restriction(s) to limit, grant, or deny access of freight vehicles to the target area. The nature of the restrictions varies in terms of vehicle type (e.g., size, weight, load factor, commodity type, or engine type), and time of travel.
These restrictions are not well received by most carriers, as they result in operational changes and higher costs. For example, the Ports of Los Angeles and Long Beach (California) have implemented a clean truck program by which trucks that do not meet certain engine configuration requirements pay a $35/TEU fee for accessing their container ports. The program expects to complete the transition to 100% clean vehicles by the end of 2013 (Port of Los Angeles 2013a; Port of Los Angeles 2013b).
Vehicle size and weight restrictions limit access on the basis of vehicle size, and often are implemented because of concerns about the perceived congestion or traffic accidents produced by large trucks. These restrictions have been recommended as a way to reduce congestion (Vleugel and Janic 2004), though noting that carriers could experience increases of about 5% in operating costs (Allen et al. 2003). Given that carriers’ profit margins are typically less than 5%, it is not surprising that most carriers oppose these restrictions. However, a growing body of research suggests that, although the look of the target area is enhanced due to the restrictions, an increase in pollution and a drop in quality of life also can result (Maze et al. 2005; Wilbur Smith Associates 2012). Using transportation models, the research has proved that vehicle size restrictions increase congestion outside the target area, an effect that could be larger than the congestion reduction within the target area (Qureshi et al. 2012; Holguín-Veras et al. 2013b).
The chief conclusion about vehicle size choice is that the private goal of carriers is aligned with the social goals of reducing congestion and pollution (Holguín-Veras et al. 2013b). If carriers use large trucks, large trucks are almost certainly the better social choice. No rational carrier would use a large truck if a cheaper small truck would do the job. Thus, if carriers are forced to replace large trucks with multiple small trucks, they are likely to increase vehicle-miles-traveled and congestion. The implication is that, to minimize social costs, policy makers should foster the use of the largest vehicles that could safely use the network without excessive infrastructure damage. Although politically controversial, this assertion is backed by strong scientific evidence (Qureshi et al. 2012; Holguín-Veras et al. 2013b). However, access restrictions motivated by the need to protect pavements and structures not capable of handling large trucks are justified, because these are externalities not accounted for by the carriers. Vehicle size and weight restrictions should be enacted if, and only if, a careful evaluation of their impacts reveals benefits larger than the costs.
It is important to draw a clear distinction between the traditional vehicle size and weight discussion concerning state and federal limitations and how metropolitan areas are impacted by vehicle size and weight regardless of their compliance with state or federal regulations. Simply, many local streets were not designed to handle the freight vehicles that are currently traversing urban areas. This creates negative externalities for both the vehicle drivers and local residents as these vehicles slow traffic to get around obstacles or damage roadways never built to withstand the weight of freight vehicles.
Failure To Remove Highway Restrictions
State departments of transportation (DOTs) typically have the massive task of keeping an inventory of every segment of roadway for which they are responsible. In keeping an up-to-date database, the DOT also must be aware of any restrictions that might prohibit trucks on their routes. Some restrictions might prohibit trucks of various sizes and configurations from using a certain road. These restrictions might be long term, because of problems with existing infrastructure, or they might be short term as a result of temporary construction. DOT staff strive to maintain an accurate list of restrictions so the highways remain safe for all users. Likewise, when a problem is fixed in the field, it is important that the corresponding restriction be removed. When restrictions are not removed in a timely manner it can create additional expenses not only to carriers, but also to other motorists and even to the end-users of the goods being transported.
An example of a restriction that was not removed in a timely manner is a bridge on New Karner Road (SR-155) over the New York State Thruway (I-90) in the Town of Colonie, New York. The bridge was the responsibility of Albany County. In Figure 6, the star shows the exact location of this bridge. In 1998, a restriction was put in place that limited use of the bridge to trucks of less than 80,000 pounds. The bridge was replaced in 1999 but the restriction was never removed from the system. Over the years, many carriers in the area contacted New York State DOT about why the restriction was still in place. Because the state DOT was not responsible for the bridge, they could not answer the question with certainty. Trucks weighing 80,000 pounds or more going between points A and B would have to bypass SR-5 because of existing restrictions. Trucks had to take SR-155 east to I-87 south. With the restriction removed, however, trucks could take SR-155 west to the Washington Avenue Extension and get to their destinations more quickly.
As shown in Figure 6, the alternative route is not a short detour, and the geometry is not as friendly to commercial vehicles. The route to bypass the restricted SR-155 bridge adds approximately 1 hour to the trip. This hour can easily cost a trucking company several hundred dollars in expenses, including wear and tear on the vehicle, fuel, driver’s wages, and reductions in the drivers’ effectiveness in relation to their hours of service. In addition, the extended route produces additional pollution, congestion, and safety impacts.
In 2013, nearly 14 years after the new bridge was placed in service, a representative from an Albany area trucking company contacted the engineer in charge of the bridge replacement project. The trucking company representative asked about the restriction, and the engineer said that to the best of his knowledge, the bridge was replaced to standard so no restrictions should be in place. The trucking representative began contacting others at the New York State DOT, and after approximately 4 months the restriction was removed. This example proves that properly documenting highway restrictions is necessary, but also the importance of making sure outdated restrictions are removed in a timely manner also is important. In this situation, the representatives from the Albany County Department of Public Works were unaware that the restriction was never removed and the state DOT was unaware that the restriction could be removed.
Truck routes specify the links of the network that can be used by freight traffic, and could be statutory or advisory (California Department of Transportation, 2012). Statutory truck routes mandate that trucks use specific segments of the network. Statutory truck routes are intended to minimize conflicts between truck traffic, pedestrians, bicycles, and local communities, as well as to protect pavements in local streets not ready for large trucks, and to discourage truck traffic in sensitive areas such as schools. Statutory truck routes should connect all major generators, allow for reasonable access to all points in the area, and minimize trucks’ need to use local streets. Valid reasons to use statutory truck routes include: to avoid structural damage to sensitive facilities, to ensure that hazardous materials are transported far from population centers, and to transport over-dimensional cargo with permits that indicate the approved routes. However, improperly designed truck routes can lead to longer delivery tours and costs. Advisory truck routes, generally welcomed by the trucking industry, inform carriers about the geometric and structural conditions of the network, allowing drivers to select the most appropriate routes. An implementation of this initiative is described in Case Study 2 in Atlanta, and Case Study 7 in New York City, presented in Section 3.
Engine-related restrictions require freight vehicles to meet an environmental standard to access specific facilities. These restrictions have been used in combination with eco-loading zones and low emission zones (LEZs), among other measures. In eco-loading zones in Bremen, Germany, or Green Loading Zones in New York City, city authorities allocated a number of parking spaces for the exclusive use of freight vehicles that meet stringent standards of environmental performance (PARFUM 2009; New York State Department of Transportation 2014). The carriers that purchase the vehicles get access to choice parking places in areas where parking would otherwise be a major challenge. This practice translates into productivity increases, because less time is wasted trying to find parking, and cost reductions due to eliminated fines.
To reduce the number of freight trips, these restrictions require a minimum load factor (percent of truck capacity being used) (Quak 2008). Regrettably, these strategies have failed to live up to expectations. The low load factors observed in most cities are the result of market conditions, not carrier inefficiencies. Basically, market pressures force carriers to minimize cargo consolidation, because doing so leads to delays that could upset customers and result in loss of business. Also, load factors naturally decrease as trucks makes deliveries. If the target area is at the end of the delivery route, it may be impossible for the carrier to meet the minimum load factor required by the city. These restrictions are also very difficult to enforce, as they require physical inspections, which in themselves produce significant congestion. For these reasons, the European cities that implemented these restrictions have since phased them out.
Time Access Restrictions
These initiatives ban freight activity during daytime hours. Typically, the ban applies to large trucks, though it could cover other vehicle types. These bans have been implemented in a number of large cities, and are bitterly opposed by receivers, who have to absorb the additional costs of receiving supplies during nighttime hours, and who consider the ban detrimental to the local economy. In response, city agencies such as those in Beijing, Shenzhen, and Changsha, China (Changsha Bureau of Public Security 2013; Shenzhen Bureau of Public Security 2013; Beijing Traffic Management Bureau 2014), and Rome, Italy, have enacted numerous exceptions to make the bans more palatable to the business sector. Feedback to the ban in Beijing indicates that carriers are unhappy because: (1) “the receivers required the shippers to deliver in the non-allowed time periods;” and (2) “they have to travel when they are told” (Beijing Traffic Management Bureau 2014). In most cases, the fines are paid by the carriers as part of the cost of doing business in the area. In Rome’s Limited Traffic Zone, trucks with laden weights of less than 3.12 tonnes (35 q) are only allowed to transit and park from 8:00 p.m. to 10:00 a.m., and 2:00 p.m. to 4:00 p.m.; while trucks with laden weights larger than 3.12 metric tons are only permitted from 8:00 p.m. to 7:00a.m. As a result, congestion and pollution may worsen, as small trucks are less efficient than large trucks (Holguín-Veras et al. 2013b). Daytime delivery bans could lead to both congestion reductions during the daytime, and productivity increases and cost savings to the carriers operating in the off hours. However, they also can lead to higher costs to receivers, which would reduce the net economic benefits. An implementation of these initiatives is described in the Case Study 1 in Atlanta, in Section 3.
Traffic Control and Lane Management
Traffic control and lane management strategies promote the effective use of available road capacity by trying to optimize the allocation of lane rights-of-way. In urban areas, where road capacity is limited, lane management often is used to improve lane utilization and mobility. By segregating trucks, which are often wider and heavier than other vehicles, mobility and safety for other road users are improved. At the same time, truck lanes reduce travel delays and improve reliability. Based on the types of users allowed in the lanes, the strategies can be grouped into restricted multi-use (shared) lanes, and exclusive truck lanes.
These lanes can only be used by a restricted set of vehicle types. Lane usage can be allocated to different users using time windows; it can be shared by all users at specific time periods; or assigned only to certain users all day. For example, Barcelona, Spain, has created seven multi-functional lanes in its commercial center. The implementation has been very successful, as it has led to an estimated reduction of 12–15% in overall travel time (SUGAR 2011), though it could confuse drivers (Ogden 1992).
Other restricted multi-use (shared) lanes are not regulated by time and allowing mixed traffic at all times. Examples are bus and truck lanes (no-car lanes), and lanes that allow buses, trucks, and high-occupancy vehicles. No-car lanes are used to segregate wider vehicles from standard size vehicles, hence improving lane mobility and safety. Because these strategies reduce travel delays, they are used as incentives for the implementation of other strategies. For example, the city of Gothenburg (Göteborg), Sweden, allows clean freight vehicles in public transport lanes, which promotes the use of environmentally friendly trucks; in the United Kingdom, Bristol allows freight vehicles that use its consolidation center to use the bus lane to foster the use of its consolidation center (START 2009,44). The lanes must be designed properly to permit vehicles to safely interact. A key decision concerns the truck types allowed in these lanes. If all truck types are allowed, too many vehicles may use the lane, increasing congestion. On the other hand, restricting the use of the lane to only select types of trucks can confusing to drivers, and enforcement is more challenging.
Another type of multi-use lane allows trucks to temporarily park in bus lanes to unload; truck travel is not allowed in the lane. An example of this type of multi-use lane is the “Lincoln” delivery bays implemented in bus lanes in Paris (BESTUFS 2007).
Exclusive truck lanes often afford a significant improvement in truck operations, with better reliability of delivery times and lower environmental impacts and risk of accidents. Exclusive truck lanes often are adjacent to general-purpose lanes, typically separated by barriers. Proposals for exclusive truck lanes in metropolitan areas are relatively rare; one of the few is a truck-only toll lane network in the Atlanta region (Georgia Department of Transportation 2007; U.S. Environmental Protection Agency 2013) and the multi-state I-70 Dedicated Truck Lane study that proved a business case for building dedicated truck lanes on I-70 across Ohio, Indiana, Illinois, and Missouri, including the Columbus, Indianapolis, and St. Louis metropolitan areas (Indiana Department of Transportation 2011).
The Handbook for Planning Truck Facilities on Urban Highways (Douglas 2004) provides a comprehensive report covering truck climbing lanes, truck lanes and truck-ways, truck-only ramps, interchange bypasses, and truck roadways and guide-ways. This report includes real-world experiences, lessons learned from previous implementation, typical issues planners face early in the planning process and a framework and methods for evaluating the benefits and impacts of truck facilities. Examples from both U.S. and international countries are presented.
Dedicated truck lanes/corridors within cities or mega-regions should be developed with a pavement management system or plan to counter the negative effects of heavy freight vehicle use. This could include a pavement plan to deepen and harden pavements on local roads that were not designed for their current uses. Many cities have managed pavement by limiting heavy vehicle access on roads that cannot support the traffic. A good example, New York City currently bans 53-foot trucks within the city. Although this theoretically would help maintain pavement quality, these policies can result in additional smaller trucks being used to meet the demand. In New York, this has created challenges for John F. Kennedy (JFK) International Airport’s ability to shift air freight to the ground mode.