You want to back that up? I would say that in certain situations building a new road is the best option.
Take Barnstaple - it was known for its traffic jams across the region, with the local radio station even producing car stickers saying 'Barnstaple - home of the traffic jam'. To put it into some sort of scale, it would often take an hour to travel two miles. So a new bypass and bridge, linking the North Devon Link Road and the main road to Ilfracombe was built, and opened in 2007, cosing £42 million. Ever since, traffic has been free flowing, with the same two mile journey now taking no more than 5 to 10 minutes. You could even argue that public transport is now a more viable option - Barnstaple Station is now much easier to get to and has a much larger car park and better bus links than it ever did before the bypass - something it could have never had before due to the old road layout.
Of course, for balance, you do have the failures - the M6 Toll may take some long distance traffic off the main M6 through Brum, but it doesn't take away any of the local 'junction hopping' traffic, and so is still congested, and indeed is having lots more money spent on installing Active Traffic Management.
The point is that different problems require different solutions. Road building can, and does work if applied correctly.
As for the original question, I think the answer is that we'd still be on horses and carts. People forget that even before cars were invented, congestion in towns and cities was terrible - you could even potentially argue that horses were our slaves. Certaintly the world was a worse place.