Q&A - Coasting Downhill

Q&A ImageQ: I often coast down a high hill in order to save on gas if there is no traffic behind me. I notice that there is a traffic offence called: "Coast down grade illegally" on the ICBC website  with a fine of $121.00 and a 2 point assessment. Is what I do coasting down grade illegally and why would that be a problem?

A: The ICBC guide Learn to Drive Smart states in Chapter 5:

"It is illegal to coast downhill in neutral or with the clutch in. You need to be in gear to safely control your vehicle."

The Motor Vehicle Act says:

Coasting down grade

197 When travelling down grade a driver must not coast with the gears of the vehicle in neutral or the clutch disengaged.

Here are a number of reasons that I found which would indicate that this is a bad idea:

  • engine braking is eliminated
  • vehicle speed downhill will increase quickly
  • increased use of the footbrake can reduce its effectiveness
  • steering response will be affected particularly on bends and corners
  •  it may be more difficult to select the appropriate gear when needed.


Going downhill in nautral (or

Going downhill in nautral (or clutch in) does not save gas, it actually burn more gas (although not significant amount) then going down hill with gears engaged. Unless you drive really old without electronic fuel injection. The reason for that is because engine in idle needs a minimum of fuel to keep running. while going down hill with gear engaged will for sure result in higher RPM than in idle so the EFI will detect that it does not need to inject any fuel to keep the engine running.

A silly thing to do!

The real irony, to my mind, is that our anonymous poster from six years back has also undoubtedly been wearing out his brakes far more quickly than necessary, apart from not saving on gas. And what does having anybody behind him have to do with his strange habit, I wonder?

Coasting downhill

We used to call this "Mexican Overdrive" but I suppose that's not acceptable any more. 

Back in the 60's, a friend had a DKW which was a weird beast. It had a 3 cylinder 2 stroke engine that required an oil-gas mixture to lubricate the cylinder walls, crank and rod bearings. Because the oil came in with the fuel, closing the throttle staved the engine of lubrication and it would sieze. It had a free-wheel clutch to disengage the front drive wheels if you lifted off.  There was an over-ride control lever to keep the wheels engaged but doing so would sometimes cause a lock-up of the engine .... not a nice feeling at speed ... and in a corner! Can you spell S C A R Y ?

I believe that the legislation prohibiting this came from the early days of non-synchromesh manual transmissions in cars and still in heavy truck manual transmissions. If put in neutral, it could be difficult to re-engage a gear and regain control. This was especially true when they had two transmissions with a jack-shaft between them.

However, newer auto-shift transmissions in heavy trucks will slip into neutral on a slight downgrade to allow the engine to revert to about a 600 RPM idle.  But it will kick the auto-throttle and re-engage if the speed climbs beyond the cruise control settings,  This permits the engine braking (Jake Brakes) to kick in and foil the "bottom of the hill" radar traps. The first time it happened to me, I was a bit non-plussed to see the tach at 600 and the speedometer at about 108. It wasn't a problem as the auto-shift system slipped it back into gear at 110.  It was set for a cruise at 105 and braking at 110.  But since the legislation had not been updated, was it illegal? Probably .....

Coasting Downhill

I once had a 1935 Standard 10 saloon with a separate control that switched in a freewheel in the transmission so that you could coast downhill to save on fuel, to be used when you didn't need engine braking. 

The engine just ticked over gently when this was in use so I find it hard to believe that fuel was not saved. The steering was not affected, and the gearlever was not moved into a different position.  I guess since coasting didn't put the gearbox into neutral or use the clutch it would not have been illegal under the BC MVA.

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