2.0 What Is Active Traffic Management – Why and When is it Used?
Active Traffic Management is generally regarded as an approach for dynamically managing and controlling traffic demand and available capacity of transportation facilities, based on prevailing traffic conditions, using one or a combination of real-time and predictive operational strategies. When implemented together with traditional traffic demand management strategies, these operational strategies can help to maximize the effectiveness and efficiency of a roadway and result in improved safety, trip reliability and throughput. A truly active management philosophy dictates that the full range of available operational strategies be considered; including the various ways these strategies can be integrated together and among existing infrastructure, to actively manage the transportation system to achieve system performance goals. This includes traditional traffic management and ITS technologies commonly applied in the US, as well as new technologies and non-traditional traffic management technologies more commonly applied in other parts of the world.
Active management techniques are utilized throughout the world, but the focus of this synthesis is on those strategies utilized in Europe and the US. While the European and US strategies are different, in many cases they are complementary and may be combined to provide greater benefits than when implemented separately. The following sections describe strategies that are used in Europe and the US to enhance and support the management of roadway facilities either in an individual or combined manner to maximize efficiency and effectiveness of a single roadway facility or a larger roadway network.
2.1 European Traffic Management Strategies
The following list provides a high-level description of strategies currently being deployed in Europe to actively manage traffic:
- Speed Harmonization/Lane Control: utilizing regularly spaced, over lane speed and lane control signs to dynamically and automatically reducing speed limits in areas of congestion, construction work zones, accidents, or special events to maintain traffic flow and reduce the risk of collisions due to speed differentials at the end of the queue and throughout the congested area.
- Queue Warning: utilizing either side mount or over lane signs to warn motorists of downstream queues and direct through-traffic to alternate lanes – effectively utilizing available roadway capacity and reducing the likelihood of collisions related to queuing.
- Hard Shoulder Running: using the roadway shoulder (inside or outside) as a travel lane during congested periods to alleviate recurrent (bottleneck) congestion for all or a subset of users such as transit buses. Hard shoulder running can also be used to manage traffic and congestion immediately after an incident.
- Junction Control: using lane use control, variable traffic signs, and dynamic pavement markings to direct traffic to specific lanes (mainline or ramp) within an interchange area based on varying traffic demand, to effectively utilize available roadway capacity to reduce congestion
- Dynamic Re-routing: changing major destination signing to account for downstream traffic conditions within a roadway network or system.
- Traveler Information: providing estimated travel time information and other roadway and system conditions reports allowing travelers to make better pre-trip and in-route decisions.
2.2 US-based Traffic Management Strategies
The following list provides a high-level description of traffic management strategies that have been typically deployed in the US.
- Ramp Metering: controlling the flow of vehicles entering a travel stream (typically freeway or highway facilities) to improve the efficiency of merging, and reduce accidents.
- Lane Management (or Managed Lane): improving or facilitating traffic flow in response to changing roadway conditions. Lane management includes controlling use of lanes by vehicle eligibility (carpool or transit), access control, and price.
- Variable Speed Limits: dynamically changing speed limit signs to adjust to changing roadway conditions, oftentimes weather related.
- Shoulder Use: use of the shoulder by time of day for transit or HOV, and in some instances general purpose traffic, to provide improved mobility along or within congested corridors.
- Pricing: managing traffic demand and flow using priced lane facilities, where traffic flow in the priced lane(s) is continuously monitored and electronic tolls are varied based on ‘real-time’ demand. Pricing of roadway facilities can collect a toll from all users of the facility. In the case of high occupancy toll (HOT) lanes, transit and carpools with a designated number of occupants are allowed to use the priced lanes for free or a reduced rate.
- Traveler Information: a variety of types of information provided to travelers (typically via variable message signs) to allow them to make informed travel decisions. Typical travel information includes travel times via alternative routes, and occurrence of incidents ahead.
The following chapters describe the listed European and US management strategies in greater detail.