My dc are at 2 different schools (Y3 and YR) and it wouldn't be physically possible to walk from one to the other in the time available between ds1 needing to be dropped off and ds2 needing to be dropped off even if i was able to persuade them to be ready early rather than late in the mornings
Walking it would be a round trip of nearly 2 hours - about 40 minutes to get to ds1's school, another 40 minutes on to ds2's school and then about half an hour home. That's assuming that ds2 who is 5 and not very sporty or good at going for long enforced walks was able to walk at a good pace for the entire distance - unlikely, especially for the first year or two.
Driving is significantly faster, not least because there are some direct dual carriage ways that I can use that I couldn't use to walk along - so even from a mileage point of view, the walk is likely to be further than the drive.
When it was snowy, the school let the parents into school 10 minutes before they usually do (ie the 10 minutes they would normally be running around in the playground in the morning if they got there early) and in the afternoon, they let people in 10 minutes before the official end of day leaving time, to make it safer and easier as they couldn't have everybody standing on the playground and they didn't want them standing around outside their front door where there is significantly less space and it would have been dangerous.
End result - huge improvement in congestion - or lack thereof, you could park in the car park or nearby easily throughout, unlike normally where you end up parking a good walk away, so much less stress and hassle. Really wish they could think up a practical scheme to have a fuzzy start and end to the day, as it could make life so much better for so many more of the people taking their kids to school!
And when I suggested it to them, they just dismissed it as 'never being able to work' - despite the fact that it had effectively been trialled already on many of the snowy days we had over the winter and shown to be successful - everybody really liked it and was commenting on how good it was as it made life so much less stressful. arrrrgghhhhhh.