Active Traffic Management (ATM) is cutting edge (at least in the US) implementation of Intelligent Transportation Systems (ITS). So then what is ITS? ITS is the application of technology (sensor, communication, processing, and dissemination) to the transportation field. It is an umbrella term that includes many specific technology such as Transit Signal Priority or Advanced Parking Management Systems.
WSDOT has been a nationwide leader in ITS infrastructure. Everyone should be familiar with the FLOW map, has read Variable Message Signs (VMS) and has been stopped by ramp meters (unless you take transit or carpool). The HOT lanes on SR-167 and the Tacoma Narrows Bridge are applications as well. ITS and traffic management systems like incident response units have been an indispensable tool for WSDOT to reduce congestion and improve travel time reliability.
The problem with all of these tools is that they respond to traffic congestion rather than actively try to manage and reduce congestion. This is were the active in ATM systems comes from. A majority of non-reoccuring congestion is caused by incidents and car crashes. The major objective of ATM is to reduce the number of crashes and significantly reduce the number of secondary crashes. This shrinks the 25% or so of congestion caused by incidents and has an added benefit of improving safety. This is accomplished by reducing speed limits when free flowing cars are approaching a backup or the freeway is close to its capacity. This strategy is also used when a crashes create a backup. This is the main focus of WSDOT’s first ATM project on I-5 NB from Boeing Access Road to I-90, and will eventually include both I-90 and the SR-520. More ATM strategies identified by FHWA are: Speed Harmonization, Temporary Shoulder Use, Queue Warning, Dynamic Merge Control, Construction Site Management, Truck Restrictions, Dynamic Rerouting and Traveler Information, Dynamic Lane Markings, and Automated Enforcement. The photo below shows most of these strategies in action, with the associated system components.
Another benefit of ATM is the ability reduce speed limits so that hard running shoulders (think SR-520 HOV lanes west of Bellevue Way) can be used during peak periods. The reduced speed limits are neccesary to maintane safe operations due to the lack of shoulders. I’m not completely versed on R8A but I think this is how WSDOT got the FHWA to agree to the lack of complete shoulders along I-90. WSDOT has a good folio with a lot of the same information.
UPDATE – Here is an interactive page that the Highways Agency in the UK made for the M42.