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MythBusters Test Right Turn Efficiency

May
20
2010

I’m a sucker for science, testing, and of course the MythBusters. On last night’s episode they tested the “right turn myth”– basically the way they framed the myth was to determine if it is more efficient to make three right turns rather than to make one left turn. Having discussed this issue several times in the past I was curious to see how they performed the test, their results, and to see if I would agree with their overall process.

The Setup

The myth was setup from the perspective of a delivery truck driver. Several locations within the San Francisco area were setup as delivery points, then two routes were derived. The first route was a more “logical” route trying not to favor right turns. This route had eight left turns, four right turns, and a total distance of 5.2 miles. The second route tried to exclude as many left turns as practical. The “right turn” route was 6.8 miles long, had one left turn and twenty-three right turns. Each route visited each stop in the same order.

The Results

The MythBusters concluded that right turns were indeed more efficient in their test. While the route favoring right turns was a longer distance and took a longer amount of time, it used only 4.0 gallons of fuel compared to 6.8 gallons of fuel on the “control” route. But I don’t think this tells the whole story…

The Route

The route they picked doesn’t really follow the premise of the myth as I understand it. For example the order of the stops was the same for both routes. This seems unnatural. While there are different levels of delivery services that demand different delivery times the order of the stops meeting those delivery times doesn’t necessarily matter. Software to construct the most efficient route could likely create an even more efficient route still favoring right turns but also allowing for strategic ordering of the stops. While I agree with their conclusion… right turns are often more efficient… the results might be even more dramatic than highlighted in their route.

Labor Costs

Another factor they didn’t consider was labor. Saving fuel does cut costs, but what about the fact that the delivery companies are paying not only for fuel, but also the salary of the driver? This is especially important as the route favoring right turns had a 17% increase in the amount of time needed to drive the route.

I dug around a little bit and found a few references to wages of delivery drivers. While it does seem to vary quite a bit, most references seemed to point to a wage of around $28/hour. The route with more left turns would result in a labor cost of about $24.27 while the route with more right turns would result in a labor cost of about $28.47 Advantage left.

Fuel Costs

Now that we are considering labor costs, let’s also consider fuel costs rather than just the amount of fuel. According to GasBuddy today’s average gas price in San Francisco is $3.12 per gallon. Using the figures provided for fuel usage on both routes, the fuel cost for the first route would be $3.54 while the route favoring right turns would cost only $2.08. Advantage right.

Total Costs

When considering both fuel costs and labor costs, I’d calculate the route with more left turns as costing $27.80 while the route favoring right turns as having an overall cost of $30.55. Using these figures, the total cost of the route favoring right turns cost 10% more than the more natural route which had more left turns.

The Premise

While I disagree with the way the myth was tested and my calculation of overall costs would dispute the myth that right turns are more efficient, I still agree with the premise that when practical, right turns should be favored over left turns. (Assuming your country drives on the right, as an astute Twitter follower pointed out.) When turning right you generally just need to wait for traffic coming from the left. When turning left you need to completely cross one lane of traffic after waiting for traffic from both the left and right. Similarly many jurisdictions allow “right on red after stop” so even if you have a light you might not need to wait. While there is no such allowance for the light while turning left.

The question should be asked like this. When building a route should you allow longer wait times for left turns or right turns? The answer of course is that turning right will generally be faster, therefore building routes that reasonably favor right turns will be more efficient.

I’m reminded of the phrase “two wrongs don’t make a right, but three rights make a left”.


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17 Responses


  1. I thought they measured their fuel consumption in pounds. They weighed the fuel cell after each run. I don’t think they converted their fuel consumption to gallons.

    Marty - May 20th, 2010
    • They didn’t, but the conversion from pounds to gallons for a known liquid is an easy conversion. I performed the conversion in my values but didn’t “show the math” as they say.

      Tim - May 20th, 2010
    • I’ll add that one gallon of fuel is about 6.0 – 6.1 pounds depending on temperature. So for my calculations where 6.8 gallons of fuel were used at a cost of $3.12 per gallon, I derived a fuel cost of $3.54 as (6.8/6)*3.12.

      Tim - May 20th, 2010
  2. I believe the software eliminated as many lefts as possible but no all together.

    David M - May 23rd, 2010
  3. Tim

    It is also my understanding that most larger companies prefer their drivers making right turn over left since accidents happens during a turn 3 times more likely making a left turn than a right turn.
    It is more of a safety issue and if it saves gas, that would add to the reasoning.

    Personally, I feel just because the Myth Buster’s say it works or don’t work, does not mean that is the truth. It’s a fun show to watch but I would not accept their findings as the gospel!

    James - May 23rd, 2010
    • I certainly don’t take what they say as gospel. I see their mission as first entertainment, second trying to get people to think critically. My goal wasn’t to prove them right or wrong– rather to get people thinking critically about different factors in route calculation and the complexities thereof.

      Tim - May 23rd, 2010
    • Wait. If you’re making three right turns to replace one left turn and the right turn accident rate is 1/3rd the left turn accident rate, won’t the overall number of accidents going from point A to B be the same? The right turn accident rate has to be lower than that to make sense from a safety standpoint.

      Eric - January 13th, 2011
      • For right turns intersection delay is usually less, but more important, crash type is much less severe when it occurs compared to a high incidence of severe crashes for left turns. When a crash happens to an employee the costs to the company are very high even if the emplyee was not at fault. For left turn errors,for any turns, the employee making the turn will most always be at fault. There is also the immediate costs and the likely increase in company insurance rates.

        Phil D - January 18th, 2011
  4. Hmmm, this is very interesting. I had never heard about the right turn myth before. It’s an interesting theory, but I agree with you that more factors must be considered when looking at whether it is truly more efficient.

    Todd - May 24th, 2010
  5. It is legal to turn right on red after stopping everywhere unless signage indicates otherwise.

    It is also permissible to turn left on a red light after stopping when turning onto a one way street. It is considered no different than turning left from a two way street into a business on the left side of the road. The key is that you do not have to cross a lane of traffic before making the turn. Turning across a lane of traffic is OK.

    Ray Thompson - June 2nd, 2010
    • Ray, my research says that isn’t correct, which is why I worded it the way I did. New York City doesn’t allow any “right on red” unless there is a sign specifically allowing it. I’m also under the impression that in California and New York you can’t turn right on a red arrow (only red circle). Likewise, I believe almost the entire European Union doesn’t allow turns on a red light unless specifically allowed.

      Tim - June 2nd, 2010
      • Your discussions make for and interesting read, but – as Tim rightly points out – all this is of no consequence to, I dare say, ‘most’ of the world (Yup: the world doesn’t end at the border of the U.S. of A., as the unenlightened [might appear to] think):
        As far as I know, it is ONLY in that single one country called the United States of America – and then not even in all of them, so-called, united states – that “it is legal to turn right on red after stopping everywhere unless signage indicates otherwise.”
        It would obviously also not make sense in the many countries where the rule of the road is to drive on the LEFT-, not right-hand side of the road. But… it remains an ENTERTAINING show to watch.

        Rudolf - June 3rd, 2010
        • For the record, right-on-red (after coming to as stop) is legal in most of Canada too (Quebec being a large exception)

          Andrew - September 19th, 2011
    • Left on red is allowed only from a one way street to a one way street, and only in the places where right on red is allowed.

      John - June 30th, 2010
  6. Different times of day may also affect the efficiency of right vs left turns. Rush hour may be particularly bad when left turns are attempted as it may take multiple cycles of the light to make the left turn.

    Yesterday I was trying to make a left turn from one street to another. After 2 miles of driving with all intersections having signs stating “No left turns between 4:30 p.m. and 7:30 p.m.” I had to give up and start making right turns.

    John - June 30th, 2010
  7. I work for one of the largest package delivery companies. Right turns only is a situational approach. In urban and busy areas this approach works best. As someone said accident prevention is much more important than cost savings since accidents for these companies aften results in privillous lawsuits. Another important aspect is to insure as much as possible that the delivery address be on the right side of the vehicle. This is a safety issue since you are not crossing streets on foot.

    The right turn approach is not as necessary when delivering in rural areas or on secondary and tertiary roads since the decreased traffic reduces chances for accidents and injuries.

    One of our most important rules is to back ONLY when necessary. Backing accidents far outnumber all others types of collisions.

    Kevin - December 19th, 2010
  8. Your point regarding the route is quite good. If applied to the rest of your analysis, the fuel costs and labor costs would likely decrease as well. Perhaps enough to make the ‘right’ route cheaper than the ‘left’ route on a purely fuel/labor basis.

    Another flaw in the experiment is that they only used one truck. Re-routing multiple trucks would obtain a synergistic result as they could adjust the coverage areas of each truck to maximize efficiency.

    David - March 25th, 2011



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