Traffic jams sometimes start for no apparent reason and can last for hours. Even a minor slowdown on a packed highway can rapidly trigger long-lasting gridlock. Traffic at times appears to act like a substance rapidly changing phase from, say, a gas to a liquid.
People driving to work to or through inner London now spend approaching 30 per cent of their time stationary and more than half their journey doing less than 10 mph - cycling pace. The last 30 years has seen a fall of average speeds in inner London of over 3 mph throughout the day - equivalent to a 25 per cent increase in journey times. Slower speeds mean more pollution, less reliable buses, problems for deliveries, more traffic using rat runs and everyone suffering more frustration and stress.
Based on observations of a German autobahn, three states of traffic on busy highways have been described : "free flow," in which traffic is light enough that drivers can freely change lanes and pass other cars; "synchronized flow," in which the roads are so clogged that drivers can't pass, but can still move; and jams. Surges of vehicles joining the highway disrupt the traffic flow enough to initiate the jump from free to synchronized flow within minutes. After being established by what might be only a brief disturbance, the synchronized flow could last hours. The researchers suggest that heavy traffic behaves like supercooled steam, in which it only takes a molecular "seed" to trigger millions of molecules to condense into water. A highway seed could be the sudden rush of drivers on an entry ramp, or drivers already on the highway slowing to admire the scenery. These apparently isolated disturbances can cause a phase transition to a state with very high density of vehicles which stays for hours on the road. Once synchronized flow is established, free-flow driving resumed only when the traffic volume had dipped to about 50% of pre-transition levels. The findings could be used to help develop traffic forecasting, highway capacity and intelligent transport systems. Modelling efforts so far have focused on average traffic levels rather than jumps between traffic states.
The London Bus Priority Network (LBPN) aims to deliver strategic benefits for passengers by promoting improvements along specific bus corridors. It will also include measures at public transport interchanges, which give priority to buses and enhanced access for cyclists and pedestrians, helping to make changes between transport services easier.
The London Cycle Network aims to provide complete links to town centres and at public transport interchanges with safer routes to schools and provision for cyclists at major road junctions.
