Seems reasonable to me.

50 mph is 264000 feet per hour. This converts to 73.3 feet per second. 300' means you need to signal about four seconds before turning or changing lanes.

Before turning, the time would be more like 8 seconds due to the need to slow down. It’s too long to be reasonable. And too much pressure to strictly adhere to the law would create perverse incentives to temporarily drop below 50MPH before signaling and to keep the signal constantly on in case one wants to pass a car. It’s better to have a reasonable law that’s easy to follow to foster a culture of high compliance rates.

Maybe the point is to be signaling before you start slowing down? It doesn't sound unreasonable to me at all.

When I turn off of rural highways with 50+ mph speed limits, I signal about the same time I let off the gas to start slowing for the turn. Braking is at least a few seconds later, turning is well after that.

It does sound reasonable if most people know where their turn is, start planning for their turn far in advance and take some time to coast before starting to brake. That’s probably what the group who wrote the law was thinking. It is not how people actually drive and it’s too far in excess of what following traffic needs to exercise caution or slow down.

One of the challenges of traffic planning is that people will do what feels comfortable and is working; it’s not really worth writing laws to force them out of that unless there’s an oil crisis or a municipal revenue crisis.

I have three primary objections, but otherwise you’re right, it’s not unreasonable.

First, signage is generally awful in Indiana. I often don’t know that I’m turning 300’ in advance.

Second, I’d prefer a rule that’s simpler to follow but still (I think) achieves the same effect for those sharing the road: start signaling at least one second before you decelerate.

Third, treating this as a money-making operation for the police is perverse.

MUTCD says this:

> In rural areas, the Junction assembly should be installed at least 400 feet in advance of the intersection. In rural areas, the minimum distance between a Junction assembly and either a Destination sign or an Advance Route Turn assembly should be 200 feet.

INDOT conveniently doesn't comply with this paragraph. You often only get a sign at the intersection itself with no advance. You're left guessing where the intersection actually is and when to slow down and signal.