Friday , 14 August 2020

Active Management Strategies for Congestion Management

Mobility challenges all over the world can be addressed by strategies like managed lanes and active traffic management. These are cost-effective methods of prolonging the life and maximising the efficiency of the infrastructure that can postpone the need for major expansion projects.

Katy Tollway Source: AARoads Interstate Guide


Congestion in urban areas across the globe is ever increasing. “Rush hour” grows longer and leads to delays, increased fuel consumption, lost productivity and related crashes. Any method to alleviate congestion can help reduce its negative impact on productivity. Transportation professionals realise building enough freeway lane capacity to provide free-flow conditions during peak periods cannot be accomplished in developed urban corridors. Cost, land consumption, neighbourhood impact, environmental concerns and other factors serve as barriers to expansion. To meet the growing demand, transportation agencies are looking at alternative operational strategies for mitigating congestion and its impact on roadway users. Two forward-thinking strategies are managed lanes and active traffic management, both of which are growing in popularity because of their potential to ease the situation.

Managed Lanes

The primary purpose of managed lanes is to improve the performance of freeway facilities. Managed lanes strategies can be applied and operated to accomplish goals in numerous areas including mobility, safety, community, finance and homeland security. All of these are ways a region can improve the overall quality of life for its citizens and ensure the long-term viability of the community.
A managed lanes facility is one that increases freeway efficiency by packaging various operational and design actions. Lane management operations may be adjusted at any time to better match regional goals, and they may also offer peak-period free-flow travel to certain user groups. According to FHWA (Federal Highway Administration), the distinction between managed lanes and other traditional forms of freeway lane management is the operating philosophy of “active management” where the operating agency proactively manages demand and available capacity on the facility by applying new strategies or modifying the existing strategies to meet pre-defined performance thresholds.

Figure1:Managed lanes - operational strategies

As shown in Figure 1, a variety of operational strategies fall under the managed lanes umbrella. While not all agencies consider all of these strategies for managed lanes, this diagram highlights those strategies that an agency might be able to utilise to help address congestion on urban freeways. In general, a managed lanes facility is a lane or a set of lanes within the freeway cross-section that is physically separated from general purpose lanes for a specific purpose. The idea is to incorporate flexibility so that operations can be actively managed to respond to growth and changing needs. The operation of, and demand on, the facility is managed using a combination of tools and techniques to continuously achieve an optimal condition such as free-flow speeds. This is done using one of three types of management: pricing, vehicle eligibility and access control. The following sections highlight those strategies that are perhaps the most common across the U.S.

HOV Lanes

High occupancy vehicle (HOV) lanes are separate lanes that are restricted to vehicles with a specified occupancy and may include carpools, vanpools and buses. Most HOV facilities require that vehicles have two or more occupants in order to legally use the facility; however, some facilities require three or more occupants during peak travel times. When implemented on freeways, three types of HOV facilities are used: Separated roadway, concurrent flow lanes and contraflow lanes. Additionally, a separated roadway facility may be either a two-way facility or a reversible-flow facility.

Value-Priced and HOT Lanes

Figure 2: Variable Speed Limits, Seattle, Washington Source: Texas Transportation Institute

The key to success for value-priced and high-occupancy/toll (HOT) lanes is to manage the number of vehicles to maximise the use of the HOV lane without exceeding capacity and creating congestion. One way to manage a HOT lane is through the use of dynamic toll pricing. The toll changes as often as every five minutes with the price of the toll increasing with the level of congestion. As the toll increases, the number of motorists willing to pay the toll will decrease, thereby managing lane use. Concerns regarding HOT lanes include legality, equity, societal issues and public acceptance.
The Katy Freeway – I-10 in Houston, Texas – has a managed lanes facility that means more options for everyone travelling in the corridor. The facility presented in the opening photograph has two managed lanes in each direction in the centre of the freeway. By taking the underused HOV lanes that previously operated on the facility and making them available to vehicles with only one occupant (those willing to pay a toll), the new managed lanes mean a more predictable trip for commuters. The facility, which opened in 2008, uses dynamic tolling, or value pricing, to vary the toll rate based on variables such as the amount of traffic on the roadway or the time of day. Tolls do not apply to HOV users during HOV hours.

Exclusive Lanes

Exclusive lanes provide certain vehicles, usually designated by vehicle type, an exclusive operational lane. The most common types of vehicles designated for this strategy are buses and large trucks. Buses are often given exclusive lanes to provide an incentive for riders by decreasing delay. On the other hand, trucks are separated in an attempt to decrease the effects of trucks on safety and to reduce conflicts by the physical separation of truck traffic from passenger car traffic. Very few truly exclusive facilities existed until recently. Many of those facilities designated for exclusive use were actually restrictive in nature, restricting trucks and/or buses to specified lanes while allowing all other vehicles to use any lane. In recent years, a number of trulyexclusive busways have been implemented in various metrop olitan areas.

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