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As part of the Highways Agency's plans to make the best use of existing roads, it is increasingly common for key intersections of the UK strategic road network to be provided with variable message signs (VMS). In the event of an incident affecting part of the network, the VMS can be used to warn drivers of the problem, and possibly to divert them onto alternative routes. Warning messages or diversions are usually selected from a library of plans, prepared in advance, to cater for a range of incidents. It can be difficult for system operators to determine which of the library of plans is most appropriate for a given incident, under the prevailing traffic conditions. To assist operators in making this decision the Highways Agency has developed MOLA (MCONTRM On-Line Assistant), a computer system able to model traffic conditions on a road network in real time and, when an incident occurs, to predict the effectiveness of alternative strategies and recommend to the operator which he should implement. (5 pages)

In August 1995, the pilot was launched of a `Controlled Motorway' on the southwest quadrant of the M25 (in the UK). The concept behind the pilot is that by controlling the speed of traffic, at times of heavy flow, flow breakdown can be delayed or prevented, resulting in a reduction in accidents, an increase in “driver comfort” and possibly an increase in throughput over the controlled section. The development of the MIDAS (Motorway Incident Detection and Automatic Signalling) system and its initial deployment on the M25 provided the basic infrastructure upon which an automatic speed control system could be built. The key feature which differentiates a `Controlled Motorway' from a conventional motorway is the use of mandatory speed limits. To ensure the high levels of driver compliance with the speed limits, the pilot includes an enforcement system which automatically detects and records vehicles exceeding the speed limit. The enforcement system was required to operate on all lanes of a four lane motorway and to enforce speed limits which vary by time of day or according to traffic conditions. To ensure that the enforcement system was always aware of the current speed limit, the signals were designed to confirm to the enforcement system, via a high integrity interface, the speed limit displayed to drivers. The M25 pilot scheme also makes use of automatic camera enforcement, using technology similar to that already proven for speed and `red light running' enforcement on all-purpose roads. (4 pages)

The SISTM (Simulation of Strategies for Traffic on Motorways) computer simulation model is being used to assess alternative control strategies, to indicate which offer the greatest potential benefits, and to determine which should be implemented on the M25. The application of SISTM to the M25 scheme has been divided into two phases: the first an upgrade to model wider carriageways, together with calibration and validation for four lanes; and the second phase the use of the extended model to assess a range of control strategies. (5 pages)