Assumptions:
Reaction time 0.68 sec,
Deceleration due to brakes 21.5 feet per sec per sec, about 2/3 of force of gravity
(These produce the Highway Code results)

Imperial

Slope 1 in 10	Stopping distances (feet)
Speed (mph)	Uphill	Level (HC)	Downhill
20	37	40	43
30	69	75	83
40	110	120	134
50	159	175	197
60	217	240	271
70	283	315	358

Metric

Slope 1 in 10	Stopping distances (m)
Speed ( mph)	Uphill	Level (HC)	Downhill
20	11.3	12.2	13.1
30	21.0	22.9	25.3
40	33.5	36.6	40.8
50	48.5	53.3	60.0
60	66.1	73.2	82.6
70	86.3	96.0	109.1

It is worth noting that the Highway Code braking figures are very conservative, and that all modern cars should be able to stop in much shorter distances. However, it is extremely doubtful that their drivers could always react within 0.7 seconds.

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