Studies of coordinated ramp signals benefits

Minimising congestion

Ramp metering signals switch on automatically to manage mainline traffic density within the available motorway capacity. The ramp metering signals only operate when needed and switch off when metering is no longer required.

The graphs below show an unmanaged motorway with congestion and a managed motorway where flow breakdown and congestion has been prevented. 

Coordinated ramp signals use a dynamic suite of algorithms that makes a combined decision based on data from the motorway and from entry ramps. The system aims to balance ramp queues and waiting times to give everyone a fair go. 

Traffic throughput and travel speed benefits

A Before and After study of the Monash-CityLink-West Gate (M1) upgrade project over 5 year periods, before and after the installation of ramp metering signals, showed reduced congestion and improved safety performance.

The operational capacity benefits included an increase in traffic greater than 56% for the length widened from 3 lanes to 4 lanes, as shown in the chart below.

If the widening accounted for an increase of up to 33%, then about 23% increased capacity can be attributed to the coordinated ramp metering. 

Safety benefits

The Before and After study showed that crash numbers, crash rates and severity of crashes all reduced despite the busiest sections having more than 60,000 additional vehicles per day in the ‘after’ period. The results show the following safety benefits in maintaining smoother traffic flow:

• Reductions in casualty crash numbers (fatal, serious and other injury) as well as the crash rate relative to the amount of travel (see chart below).
• A reduction in crash rates, even though crash rates on other unmanaged Melbourne motorways generally increased. This was achieved even with higher average speeds (+20km/h).  

Further detailed reading is also available in the various Traffic engineering manuals and Managed Motorways Framework - March 2017 [PDF 21Mb]