摘要: |
By unpacking the various components of smart motorways, it may be possible to work out which has a future and which should be consigned to history. The ability to slow down or stop traffic approaching stationary vehicles using CCTV and sensors seems to provide both safety and congestion benefits. Emergency areas (EA), which allow some stranded vehicles to get off the carriageway altogether, are safer than the hard shoulder -though it is even safer to have them work with a hard shoulder. National Highways says it has never had a fatality in an EA. The concrete central barrier that is standard on all lane running schemes (ALR) also provides a significant safety benefit and, to its credit, when it first paused new schemes last year, the Government said it would nevertheless continue to install these on the stretches that had been due to be converted. However, National Highways recently cancelled a planned barrier upgrade on the M62 after costs rose (see page 9). ALR schemes aim to tackle congestion through the extra lane with a potential safety benefit from spreading out the traffic. However, does this survive the well-established phenomenon of induced demand - where additional capacity is lost to additional vehicles? |