No to faster motorway speeds.

Driving fast is fun. I’ve enjoyed Italian and French motorways at 130km/h, and the Germany Autobahn at the maximum speed attainable by the small Nissan I was driving (~190km/h).

But is it a good idea? For new motorways in New Zealand?

Assuming a car was able to travel at *exactly* the speed limit, the time savings for travelling 10km would be 33 seconds off a 6 minute trip. That doesn’t seem entirely bad. But in some sort of real world analysis (not formally published) a change of limit of 10mph led to an actual increase of only 3-4mph (author information here), so I think it is safe to assume the real world time savings might be less.

Assuming incrementally New Zealand continued to increase the quality of roads, an increased speed limit would save you 2 minutes 21 seconds from the start of the Northern Gateway to the Auckland central motorway junction (CMJ, 43km), assuming, haha, no congestion. Or all the way through to Pokeno (95km) 5min 11 sec. Or if Auckland CMJ to Hamilton was one long stretch of 110km/h. Savings 6 minutes 26 seconds. In. No. Traffic.

If that isn’t bad enough, most negative events associated with driving increase exponentially rather than linearly with increasing speed. So we have a nominal increase of 10% in the speed limit, but potentially less than 5% actual speed increase, but with more than 10% increase in fuel consumption, and a higher than 10% likely increase in crashes and fatalities.

Oh, and having vehicles travelling faster actually means less cars able to fit on the road, so more congestion.

In international contexts, truck drivers are not interested in travelling faster, realising that the miniscule time savings are more than outweighed by the increased fuel consumption.


About James

I'm a scientist. Sometimes I get distracted.
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