Dáil Éireann Debate, Tuesday - 14 May 2019
420. Deputy Thomas P. Broughan asked the Minister for Transport, Tourism and Sport if research has been carried out into the improved lower carbon emissions that would result from lower speed limits on roads here; if data are available on the issue in other EU jurisdictions, the United States of America, Canada and Australia; and if he will make a statement on the matter. [20389/19]
Amharc ar fhreagraResearch in this area does suggest that energy use increases at higher travelling speeds; some studies suggest that moving from 100km/h to 120km/h increases fuel consumption by up to 20% and reducing speed limits, particularly on the motorway network, is often suggested as potentially having a role to play in reducing transport emissions. Co-benefits for road safety may also arise. However, negative economic impacts, reduced fuel tax revenue, and longer travel times are noteworthy concerns. It is also possible that a proportion of the motorway traffic would divert on to secondary networks as a result of a reduced speed limit. Reviews to the design speed for existing infrastructure and speed enforcement procedures would be required in light of any proposal to lower speed limits.
The Deputy may be aware that reducing speed limits on motorways has been identified as a possible longer term transport mitigation measure in the National Mitigation Plan (Measure T24). My Department officials estimated the impact of reducing maximum speed limits on motorways from 120km/h to 110km/h for cars/vans and from 90km/h to 80km/h for heavy goods vehicles compared to current speed limits and estimated that cumulative total greenhouse gas emission reduction savings of 1,881 tkCO2 were possible over the period 2017-2030.
Implementing such a mitigation measure would require a full detailed review of the potential economic, safety and societal implications as well as an assessment of the likely environmental impact. Concerns also exist regarding the potential erosion of the considerable economic benefit derived from substantial motorway investments made to date. It should also be highlighted that National Strategic Outcome 2 (Enhanced Regional Accessibility) in the National Planning Framework commits to improving average journey times for connectivity reasons. The Framework targets an average inter-urban speed of 90kph. A reduced motorway speed limit may be in conflict with to this aim.
I would draw the Deputy’s attention to the fact that actual fuel consumption benefits of lower speed limits for motorway drivers is dependent on a number of external factors such as vehicle types; driving patterns; the frequency of speeding; road load patterns; and congestion levels. I am given to understand that carbon savings from lower speeds can also vary markedly depending on engine characteristics; vehicle weight; distances travelled; and supplementary equipment such as rear mounted storage racks or even taxi signs.
While some limited research has been conducted at EU level and in other jurisdictions, there continues to be a lack of official and scientifically robust data on this issue. I am, however, committed to the ongoing exploration of all mechanisms available to reduce emissions and encourage more individuals to move towards decarbonising the transport sector.
It is also noteworthy that the vehicles we drive and the fuels that power them are themselves steadily becoming less carbon intensive. The penetration of renewable biofuels as a share of road transport energy has increased significantly over recent years. In 2017 alone, biofuels blended in fuel reduced CO2 emissions from vehicles by an estimated 457 kilotonnes. A further important role is played by ever more stringent efficient standards for vehicles. Such developments will erode emissions reduction benefits of reducing speed limits. Through better technology, improved efficiency and higher biofuel use vehicle emissions are being decoupled from increased economic activity and population growth.
