Earlier this week we published instructions on how to disable daytime running lights on a second generation Tundra, and one of the first comments on that post was, Why disable daytime running lights in the first place?

My initial response was “why not?”, but that’s really not much of an answer. So, I did a little digging into the safety benefits of daytime running lights. Here’s what I found:

1. Daytime running lights aren’t required in the USA, but they’re quite popular in Europe and Canada. Canada, Denmark, Finland, Hungary, Iceland, Norway, and Sweden all legally require vehicles to have daytime running lights. In the US, GM made daytime running lights a standard safety feature starting in 1999, and a lot of other manufacturers (Lexus, Mercedes, Saab, Subaru, Volvo, VW, etc.) have done so as well.

2. Multiple studies indicate daytime running lights work. According to a series of studies conducted in Norway, Denmark, and Canada, daytime running lights:

• Reduced daytime crashes between 6-11%
• Reduced left-hand turn crashes by 34%-37%
• Reduced crashes involving pedestrians by 28%
• When crashes did occur, the severity of the crashes was lower on vehicles with daytime running lights (slower speeds)

3. Despite study results, there are many doubters. While multiple studies conducted by governments and private entities around the world seem to indicate that daytime running lights are a safety feature, there are critics of daytime running lights who say:

• Many of the studies that found daytime running lights offered a significant safety benefit were conducted in Canada, Norway, and Denmark, where light levels are different compared to the rest of Europe and North America.
• Many of the studies used relatively small samples.
• Many of the studies were conducted as other safety features were added. Anti-lock braking systems, for example, were being added to vehicles at the same time that daytime running lights where being tested.

4. NHTSA’s most recent study finds no significant benefit to daytime running lights. It’s a little hard to track down, but NHTSA technical report HS 811 029 (pdf) states:

This is the third statistical analysis conducted by NHTSA to evaluate the effectiveness of daytime running lights (DRLs)…the analysis found that DRLs have no statistically significant overall effects

NHTSA’s study did find that daytime running lights reduced light truck crashes about 5%, but otherwise they had no statistically significant impact on safety.

What Does It All Mean?

So, how can these differences between studies be explained? The NHTSA report explains that many of the older studies used a less reliable statistical model (simple odds) rather than a more statistically robust “ratio of odds” method. The NHTSA study also mentions that the definition of “daytime” may differ between studies. If we try to apply a little common sense here:

1. There is no statistical safety benefit to daytime running lights during daylight hours, but there’s no conclusive data about their effectiveness during dawn and dusk.
2. While earlier studies have flaws, it must be acknowledged that daytime running lights seemed to be more effective in Northern climates where natural light isn’t as bright.

Anyone else see a pattern here? During low-light conditions, headlights seem to be a good safety feature.

No kidding.

Read more about daytime running lights here:

• http://www.ibiblio.org/rdu/DRLs/studies.htm
• http://www.iihs.org/research/qanda/drl.html
• http://www.usroads.com/journals/rmej/9912/rm991203.htm
• http://en.wikipedia.org/wiki/Daytime_running_lamp

Check out this list of available Toyota Tundra shocks