I sort of accidentally stumbled into it when I joined an (at the time) startup as they were just getting into the market. So I don't know that I have anything specific to offer :)

I don't want to name names for companies in the industry, but you can find them in industry publications like Traffic Technology Today, or often as contributors to the standards documents like NTCIP 1202, ITE ATC 5301, etc.

I will say that there are a number of long-standing (40+ years) companies in the industry that seem to still operate the "legacy" way - slow iterations, very small software team, seemingly not much desire for large change. Basically, a hardware company that also happens to sell software.

There are also newer entrants to the market in the past ~decade or so that operate a lot closer to a modern software company - lots of new features coming out, fast-moving software teams, etc.

(again, all opinions are my own here.)