Up to Speed, Thinking Highways, Dec 2010
A feature article on the impact of variable speed limits appears in the latest edition of Thinking Highways magazine. TSS’s Gabriel Funes and Alexandre Torday discuss a prestigious project with the Servei CatalÃ de TrÃ nsit (SCT, the Catalan Traffic Department), where Aimsun software was used to model and evaluate the already operational variable speed limit system on the C31 and C32 access road to Barcelona and also the projected system on the A2 and B23.
Funes and Torday demonstrate that the mixed results with regard to reductions in journey time generally showed that the degree of improvement in journey times depends on the degree of congestion. That is, the greater the congestion, the greater the benefits of variable speed limits. In situations with only mild congestion, variable speed limit systmes can â€œover correctâ€ and actually be counter-productive in terms of reducing journey times (although this should not take away from their usefulness in combating fuel emissions, which were significantly reduced across the board).
Another area where variable speed limits consistently bought about a marked improvement is for the parameters of the frequency and duration of stops. In the case of the C32 model, with the variable speed limits system, there was an average of 35-40% fewer stops and the remaining stops were 60% shorter. Similarly, the B23, the A2 and the C31 all showed improvements of 20-34% in stop frequency and duration.
The comparison of the current situations with the Aimsun models showed that variable speed limits are highly effective when applied in the right place and at the right time, with the result that the SCT could consider the implementation of variable speed limit systems across more of the Barcelona network.
Please click here to read the article in full.
© 2010 Reproduced with kind permission from Thinking Highways magazine of H3B Media.