The most common modifications cities are doing to roads that are easy to speed on is to add either:

• sidewalk extensions, narrowing the road at the most crossed point;
• speed bumps, as seen here;
• and/or chicanes, which break up the straight and require a driver to be more active in their steering.

All these techniques are effective at slowing cars down on straight roads.

It’s a wide straight road which invites people to drive faster

If you want them to slow down automatically, make the road smaller. People will slow down. Swerve the road slightly, people will slow down. Needs it to be a slow road? Put obstacles left and right requiring the cars to swerve slowly

There are great many ways to build roads, the USA doesn’t have many