Multi-objective optimal speed for expressways

Sze-Hwee Ho, Yiik-Diew Wong, Victor Wei-Chung Chang

Research output: Contribution to journalArticleResearchpeer-review


Relationships for speed-flow, speed-fuel consumption (speed-carbon emission rates) and speed-accident occurrences for highway (expressway) driving conditions are reviewed. The optimal speeds for maximising traffic flow capacity on highly utilised expressways in Singapore lies in the range of 4565 km/h, a speed band that the Land Transport Authority (Singapore) uses in its Electronic Road Pricing (ERP). On the other hand, the optimal speed range lies between 50 and 75 km/h based on efficient fuel consumption. As for carbon emission rates of the vehicular flow, the optimal speed range is 5060 km/h. In terms of accident occurrences, the general norm is that low travel speeds as well as low speed variability are desirable. Experimental runs have shown that a relatively low speed band is preferred for greater fuel efficiency. Setting operating speeds that straddle the optimum regimes of capacity, safety and environmental sustainability suggests a range of 5060 km/h.
Original languageEnglish
Pages (from-to)80-88
Number of pages9
JournalThe IES Journal Part A: Civil & Structural Engineering
Issue number1
Publication statusPublished - 2015
Externally publishedYes


  • optimum speed range
  • traffic flow capacity
  • fuel efficiency
  • carbon emission rate
  • fuel economy

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