‘Costs’ and ‘benefits’ of 80 mph speed limits

2 Mar

The government is wanting to increase motorway speeds from 70mph (112km/h) to 80 mph (130 km/h). The Transport Secretary explains: “We need to do this on a pretty rigorous cost-benefit analysis basis…at the moment there are a clear set of criteria for making these decisions. Perhaps we ought to ask if we are using the right set of criteria”.

Netherlands is also planing to increase it’s motorway speed limit to 130 km/h while Spain is currently lowering its speed limit from 120 km/h to 11o km/h to reduce fuel imports! Check out this useful blog post on the subject confusion that we are in at present.

Lets do a rough and ready cost-benefit analysis given that both the ‘costs’ (ie mainly injuries, deaths) and the benefits (mainly a few minutes off journey time for car drivers) can be reasonably easily calculated so lets have a go.

For every 100 miles driven one will save 10 minutes in travel time (75 mins, down from 85 mins). This does of course depend on having a clear road and no holdups due to crashes.

Lets look at the ‘costs’. According to a review of changes to speed limits conducted for the authorities in British Columbian 2003 the rate of crashes and fatalities is likely to increase significantly. They don’t report on any countries increasing speed from 70 mph to 80 mph (110km/h to 130km/h). They do however report on when Switzerland reduced its speed from 130km/h to 120km/h with reduced fatalities by 12% and when Sweden reduced speeds from 110km/h to 90km/h and fatalities declined by 21%. Also interestingly when the UK reduced speeds from 100km/h to 80km/h  and saw a reduction of 14%.

By contrast when Australia increased its speed limit from 100 km/h to 110 km/h it saw an increase in fatalities of 25%. Increasing speeds in the USA from 89km/h to 105 km/h often had associated increases in fatalities of about 20%.

The Wikipedia Road Safety Article has a useful table which shows motorway casualty rates in the first column and speed limits in the right column (this is not properly referenced though). Is it just me or is it significant that all the worst countries have high speed limits and all the most safe countries have low ones?

Speed safety stats

Do also check the excellent UK Speed Limit article which has a lot of detail of the history of UK speed limits and which is fully referenced.

So, lets get back to an estimate of the ‘costs’. In 2008 there were 158 fatalities on Motorways. As a rough indicator based on the above research, it looks like we can expect about 30 more fatalities. There are many other costs not yet considered including: increased fuel usage, more road noise, more carbon emissions, more stress, more delays caused by crashes. These concerns are echoed by the AA Trust who warned back in 2005 against a blanket increase in the motorway speed limit to 80mph saying that in the absence of strict enforcement to would lead to “unacceptable enforcement drift to 90 mph” – which would “increase the risk of accidents and raise the total of fatal and serious injuries”.

Incidentally, almost half of UK drivers wanted vehicles to be fitted with Speed Limiters which are already used on trunks which are limited to 56 mph and on express coaches at 65 mph which will also be using the motorways.

There there is the research study conducted by the Institute of Advanced Motorists and the RAC Foundation back in 2006 found that some 26% of motorway drivers were following the vehicle in front too closely and that on the M4 the figure was 50%. Do we really want people tailgating at 90 mph?

The ‘cost’ is some 30 deaths and more crashes, which, errr.. might actually reduce the benefit by creating more hold-ups. Also, increased road noise, fuel consumption and driver stress. The benefit is some 10 minutes off journey times per 100 miles (assuming that there are no congestion, road works or crashes to contend with).

At this point transport consultants would convert these costs and benefits into money using standard calculations used by transport planners. I won’t do this because I don’t have the figures to hand and I find the idea rather offensive.

Finally, here is a chart showing road deaths on UK roads since 1929. Be aware that it was a nasty Labour government that introduced the 70mph speed limit in the 1960s after some terrible crashes in fog. since then fatalities have reduced impressively over the past 40 years under both Labour and Conservative governments. Is this trend going to continue going down or are all these ‘motoring’ biased initiatives (such as removing school crossing patrols, re-timing lights in favour of motorists, increasing speed limits, cutting back on bus services, bus lanes and cycle lanes), are we going to see the graph turn up again. I do do hope that this in not going to be the case.

Killed on British Roads

What I would like to is see now is someone doing a FOI request on the Department for Transport requesting their official report on the subject. There is the nice WhatDoTheyKnow website that makes this very easy to do.

14 Responses to “‘Costs’ and ‘benefits’ of 80 mph speed limits”

  1. David Hembrow March 2, 2011 at 11:05 am #

    Unusually, this is an area where the UK and the Netherlands are doing the same thing. It’s been summed up here as nothing else than a cheap way to please some voters.

  2. Amoeba March 3, 2011 at 9:01 am #

    As David said. Essentially, it will wosen transport pollution, which will increase transport related deaths. It will worsen carbon emissions for a tiny potential increase in traffic flows. It’s inevitable that it will lead to significantly more energetic road collisions. Traffic flows may actually decline due to dynamic traffic flow effects, but I’m rather less certain about that.

    All in all, it’s a cave-in to the ignorant Daily Mail reading motoring lobby.

    What happened to science and research-led policy?

    • Peter Miller March 3, 2011 at 6:49 pm #

      Another consideration that has occurred to me is that drivers wishing to travel at 80mph will feel it is their ‘right’ to go at that speed in the outside lane. On a 3-lane road a truck speed limited at 56mph or an express coach speed limited at 5mph will equally feel it is their ‘right’ to use the middle lane. Someone wishing to travel at 70mph will therefore be pressured back into small gaps in the 2nd lane on a frequent basis. Their only other option being to speed up to the speed limit.

  3. James C. Walker March 17, 2011 at 4:18 pm #

    The predictions of saved travel time and more casualties are simply nonsense. Per the DfT, 85% of the free flowing traffic NOW travels at 79 mph or below. Thus, resetting the posted limit to 80 or 1 mph above the 85th percentile speed will make traffic flow smoother and safer, it will NOT materially change the actual travel speeds because they are already in that range. It is extremely unlikely that the 85th percentile speed will change by more than 1 or 2 mph at the most, so no significant time will be saved and no significant risks will be added. You can read the science at our website or the Association of British Drivers website. Regards, James C. Walker, Board Member-National Motorists Association Foundation, http://www.motorists.org, Ann Arbor, Michigan USA (and a frequent visitor to Britain to see my wife’s family in West Yorkshire)

    • Peter Miller March 22, 2011 at 6:53 pm #

      I have approved the above comment even though I don’t agree with it or believe that their ‘science’ is scientific. Both organisations are climate change skeptics which is never a good start!

      The Wikipedia article for the Association of British Drivers (http://en.wikipedia.org/wiki/Association_of_British_Drivers) is pretty revealing as is the associated talk page (http://en.wikipedia.org/wiki/Talk:Association_of_British_Drivers). The Wikipedia article and talk page for the National Motorists Association is also interesting (http://en.wikipedia.org/wiki/National_Motorists_Association).

      For the real evidence on speed limits and safety the Wikipedia Speed Limit article (http://en.wikipedia.org/wiki/Speed_limit) and associated talk page is useful. The article has been worked over at great length and now provides a good overview and set of references. There were however massively long and fruitless discussion on the talk page from a few people arguing that the World Health Organisation was not a reliable source for road casualty figures (they lost)! Lots of other nonsense on the talk page as well and as such it is a very useful resource about what people will argue about.

      Fyi, I will not approve any further comments on this blog which promote this more extreme “Motorist’ viewpoint as such views can easily be found elsewhere on the web and I know that no one is about to change their views on the matter.

  4. Si April 27, 2011 at 9:23 pm #

    I don’t think it will increase the speed limit overall, but the ones that will increase are probably the most dangerous – and that is the type that will drive at the limit regardless of conditions and assume that anyone else that doesn’t should get out of the way.

    I still don’t think it should be increased though – our “the limit is 70, but we won’t book you below 90″ approach is okay as it still allows the police to book someone for doing 75mph if they would have trouble pinning down dangerous driving on someone (a kind of backup).

    Granted 90 can be too high sometimes, specially with all the major bad tailgating going on – and I have been tailgate by the police before on minor roads at a good speed.

  5. James C. Walker April 27, 2011 at 10:04 pm #

    I have studied some sections of Interstates (Motorways) in Texas posted at 80 mph in areas with far less population density than any area near any Motorway in Britain. These are RURAL areas, huge counties with maybe 40,000 total population. The 85th percentile speeds range from 82 to 84 mph where your visibility is well over 1 mile and the nearest vehicle to you is over .5 miles away. The percentage of drivers over 90 was almost non existent. James C. Walker

    • Peter Miller May 1, 2011 at 5:34 am #

      Thank you for you further comment and I apologise for my possibly over-abrasive earlier response which prompted more by the ridiculous and irresponsible views expressed by the Association of British Drivers over the years than by anything you said – other than mentioning their name!

      It is certainly interesting to compare Texas and the M1 motorway in the UK. My experience of the USA recently (from the saddle of a bicycle in Detroit of all places) is also that Americans take pride in being considerate drivers and take every opportunity to slow down and stop for pedestrians and cyclists as well as other motorists. That is so different from the UK where I am confident that a significant minority of motorists would use a higher motorway speed limit as their ‘right’. They would pressure drivers in the fast lane driving at under 80 mph to move over by tail-gating them; They would also consider it their right to exceed this limit by 5-10 mph without getting a ticket from the police as a matter of ‘fair-play’.

      I think there is e huge difference in culture as well as the traffic volumes between Texas and the UK.

      • James C. Walker May 1, 2011 at 3:52 pm #

        I took no offense, Peter, on your earlier comment. It is interesting to see how much our personal views differ. I consider most British drivers to be FAR more courteous than average American ones, with Texas drivers being the exception because they are almost uniformly the best in the USA for courtesy. I agree that with 80 mph legal limits the drivers coming up from behind would pressure drivers in the fast lane to move over – and for me this is precisely proper. Slower drivers have no business cruising at slower speeds in the fast lane when open space exists in the slower lane(s) to the left. This is the secret to the high level of safety on de-restricted Autobahns where the speed differential can be 50+ mph between the slowest and fastest drivers. Lane courtesy or lane discipline is one of the keys to Motorway safety and the smoothest traffic flow with the fewest conflicts between vehicles. In general, I find British drivers to be FAR better at this courtesy than most American ones. Also in general, realistic speed limits help promote this safer behavior. With 85th percentile speeds at 79 mph on British Motorways, I find no reason to leave the posted limit at 70 to define perhaps 85% or 90% of all drivers as criminals and to encourage drivers at 74 mph to block the fast lane causing more tailgating, aggressive driving, passing on the left, and other driving risks. It is NOT the job of slower drivers to enforce posted limits, that is strictly a police function. The Michigan State Police who I work closely with want slower drivers to move over so the crazy driver at 90+ mph will have a clear shot at the fast lane and THEN they can find and cite those drivers who are way above the normal traffic speeds. When slower drivers “play copper”, their job is much harder. Regards, James C. Walker

      • Peter Miller May 4, 2011 at 2:40 pm #

        So you believe that motorists wishing to travel at over 70mph will have a moral right to push other motorists into slower lanes in with lorries doing 56mph or speed up to 80mph? Thanks! I don’t want that and nor, I am sure neither do the rest of the 85% of motorists who travel travel at less than 79mph and who have actually slowed down already in response to higher fuel prices. http://uk.autoblog.com/2011/02/24/higher-fuel-prices-slow-down-motorway-speeds/

  6. James C. Walker May 4, 2011 at 3:04 pm #

    I understand your view, Peter, and it is not uncommon. That said, it is the rule or law in most places that slower traffic on multi-lane roads is to yield the fast or passing lane to faster traffic. It is also one of the most fundamental rules of traffic safety, whether the speeds involved are legal, or not. It is normal on a de-restricted German Autobahn to see a Porsche at 100+ mph pass a lorry going 62 mph, and then move ALL the way back to the right hand (slowest) lane where space permits. If someone wishes to drive below the normal speeds of travel to save fuel – that is GREAT – but they have no business doing so in the fastest passing lane. It is bad driving and increases danger for all users. Regards, James C. Walker

    • Peter Miller May 4, 2011 at 3:15 pm #

      To rephrase the above: anyone wishing to travel at less than the fastest speed (not the ‘normal speed’ as you suggest) has no right to use the outside lane if someone wants to go faster even if the other lanes are busy with slower traffic. If they don’t then they will be responsible for any accident, not the person pushing through. Thanks. Don’t you just love ‘Motorists with a capital M’. Have a nice day and enjoy Texas.

  7. James C. Walker May 4, 2011 at 4:05 pm #

    Blocking the passing lane does not typically cause an accident right at that time and location. It DOES cause disruption in the normal flow of traffic, and is illegal in many venues around the world. Blocking the passing lane unnecessarily is one of the principal causes of aggressive driving and even road rage. That said, if the lane(s) to your left on a British Motorway are close to full when the road is near its flow capacity and moving over would be difficult or impossible, then the move-over rule does not apply. But, when the car in the fastest passing lane encounters a vehicle blocking that lane AND room exists in the center and/or slow lanes for them to move over, then it is the fault of the slower car if they do not move over. If you watch German drivers on de-restricted Autobahns, they almost all behave properly. When there is room to move to the slower lanes, even when they are at 100+ mph, most will do so — yielding the passing lane to the occasional car at 120+ mph. This sort of behavior provides the smoothest and safest traffic flow. Texas drivers almost all display this same level of courtesy and safe driving. Regards, James C. Walker

  8. Peter Miller May 4, 2011 at 4:13 pm #

    I suggest we close comments to this blog post now as we have both the Motorist view and the road safety view well presented and there is little to be gained from further discussion.

    I will delete any further comments from people who are approved to contribute and will refuse comments from any other sources.

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