Does speed directly affect driving rolls?

[clu2415]

Is there a speed penalty to driving or is it a case of not being able to avoid what you can’t see? If you’re heading toward a pothole at 80 mph, that -8 to perception is significant.

Also, does a wheeled character make acrobatics rolls instead of driving?

[Varyon]

I'd say no. The examples for Task Difficulty (B345) differentiate between a car chase and a high-speed (emphasis in original) car chase at only a -1. Speed can be a big influence when you need to make a tight turn, of course, as the faster you're going relative to the vehicle's acceleration, the wider of a turn that's required (see B394-396). In theory, I suppose you can require a roll against Vision to see a pothole or whatever when it's 0.5 seconds away (average human reaction time to visual stimuli is 0.25 seconds, this gives you time to do something), such that higher speed means having to spot the obstacle from further away, but that's probably overkill. As an example, a ~2-foot wide pothole, it's wider than it is long (or at least looks that way from the driver's seat) is SM -3. It's in plain sight (unless the GM decides it blends in, say due to recent rainfall), for +10, for a total of +7 to see it. At 30 mph (~Move 15), you need to spot it from 7 yards away to be able to appropriately react in time, for another -3, and a total of +4 - a typical person has a 90% chance to spot such a pothole. Of course, if you aren't paying a lot of attention to the road (which is going to apply to most drivers), the "situational awareness" check suffers a -4, for a net +0 (50% chance to spot). At 60 mph (~Move 30), you instead need to spot it from 15 yards away, for a further -2 relative to the above - someone paying attention has a ~74% chance to notice in time, someone who isn't has a ~26% chance. Again, this is overkill for most games, but looks like it would roughly pass the sniff test.

[clu2415]

My situation is that a PC wants to drive 80 mph over a highway with zero maintenance for 50 years. But if road conditions are that bad, sometimes the only way to avoid a wipeout will be to slow down and go around. Hence the maximum speed modifiers for terrain.

[Varyon]

Originally Posted by clu2415

My situation is that a PC wants to drive 80 mph over a highway with zero maintenance for 50 years. But if road conditions are that bad, sometimes the only way to avoid a wipeout will be to slow down and go around. Hence the maximum speed modifiers for terrain.

See Ground Travel, B466. I'd say an unmaintained highway probably counts as Average, and may no longer count as a road (in which case you use Acceleration x4 rather than Top Speed). The vehicle can go 60% faster with hourly control rolls (failure of which risks a wipeout); I'd be tempted to crib from the rules for Time Spent (B346) to go faster than that (up to the vehicle's top speed), basically dividing the +60% speed by the desired speed to get how much time you are spending.

For example, let's say the character is driving a TL 7 Sports Car (B464; Move 5/75). If you let the highway count as a road, safe travel speed is equal to 0.5*75 = 37.5 mph. This can be boosted to 60 mph with hourly control rolls. Boosting this to 80 mph means taking 60/80 = 75% as much time, which calls for a -3 to Driving. If you instead decide the highway doesn't count as a road, safe travel speed is equal to 0.5*4*5 = 10 mph. This can be boosted to 16 mph with hourly control rolls. Boosting this to 80 mph means taking 16/80 = 20% as much time, which calls for a -8 to Driving. In either case, the maximum possible speed is around 150 mph (-6 in the first case, -10 in the second).

I wouldn't really have spotting potholes and the like apply here, although if you're tracking things second-by-second (as in a combat situation), you might want to see if anything is usable from my first post.

Oh, and as for the question I initially missed, a character usually makes control rolls (when needed) for itself at DX+3. Letting a skill substitute for DX is probably fine, with either Running or Acrobatics probably working for ground movement (including those with wheels, those that bounce/roll/slither, etc), Flight or Aerobatics for flying, and Swimming or Aquabatics for swimming. The +3 would still be in play; this is essentially a character's Hnd score.

[clu2415]

Ah, I like that approach. Thanks.

[Kale]

You might also consider a failure on that driving roll to mean that they drove through a rough patch really hard. This could require the vehicle to make a HT roll to avoid suspension damage. If it takes enough damage you risk wrecking the car. Could be a good alternative penalty to a failed roll instead of just having them wipe out or go slower.

[maximara]

Originally Posted by clu2415

My situation is that a PC wants to drive 80 mph over a highway with zero maintenance for 50 years. But if road conditions are that bad, sometimes the only way to avoid a wipeout will be to slow down and go around. Hence the maximum speed modifiers for terrain.

Depending on the country the road may have not been designed for those speeds. For example, many state highways in the US could at best handle 70 mph. Roads in mountains use switchback and trying to do anything over 50 mph on those is akin to going 'I'm tired of living'.

Also there many not be a road there. Back in the 1990s I travel on an old BLM road to Mt Trumble, AZ (a ghost town since the 1960s) and the mountain road we used to get there was literally falling apart (it required a 4-wheel drive to transverse) and if not for the work that clearly went into getting it back up to snuff I doubt it would be anything resembling functional condition today in 2020.

[Varyon]

Originally Posted by maximara

Depending on the country the road may have not been designed for those speeds. For example, many state highways in the US could at best handle 70 mph. Roads in mountains use switchback and trying to do anything over 50 mph on those is akin to going 'I'm tired of living'.

Of course, posted highway limits are typically set with typical cars in mind, so if the PC is driving a sports car with ~0.5G acceleration as in my example, the curves can be handled at a higher speed (although that's a pretty bad idea, particularly if there are other cars on the road). A curve a ~0.2G sedan can handle at 50 mph is one a ~0.5G sports car can handle at 125 mph, at least under GURPS rules.

[AlexanderHowl]

At 80mph, I would require a HT roll every minute for the car. A failure on the HT roll would deal damage equal to the margin of failure to the car, th cargo, and its passengers (times HP/10, rounded down) as they are banged to pieces by it hitting the potholes.