Experimental Mode assists¶

In Experimental Mode, set speed is a maximum. Speed Assist can raise the model's speed on a clear road; Lead Follow Assist can close an excess gap behind a steady car. Both are off by default.

openpilot's planner takes the lowest of the model's acceleration, the following-distance controller's and the cruise controller's. Both assists adjust only the model's value, so the set speed stays a hard ceiling.

1. Speed Assist runs when no car is ahead. It lifts the model toward your target speed: the set speed, or a lower limit from Slow for Curves or Speed-Limit Assist. It closes the gap in about 6 s, at most 0.8 m/s².
2. Speed Assist gives the speed back. The model keeps speed it did not choose, so added speed would carry into the next bend. Speed Assist reads the model's plan and works out how fast the car may go and still ease gently into each bend, stop or slowdown ahead. Over that limit it hands back what it added, never more, at up to 0.6 m/s².
3. Lead Follow Assist runs behind a steady car. It lifts the model toward the following-distance controller, which holds your Driving Personality gap. It fades in as the extra gap grows from 3 m to 10 m, and can at most match that controller, so it never follows closer or speeds up harder than chill mode would.
4. The model keeps the last word. Both assists fade out as the model starts to brake, so the car settles where the model pushes back.

what you'll notice¶

• Clear road. The extra speed builds within a second or two and holds.
• Bends and stops. The added speed comes off a few seconds before the model's own slowdown. Speed Assist never makes the car slower than the model alone, and never adds speed that would take a bend past 1.0 m/s² of sideways acceleration.
• Behind a car. The model matches the lead's speed but mostly ignores the gap. Lead Follow Assist closes extra gap beyond your following distance, up to a cap per personality:

• Low speed. Both fade in between about 11 mph (18 km/h) and 18 mph (29 km/h), so stop-and-go stays the model's.
• Limit. Some driving models plan a slowdown as soon as they pass their own pace. Speed Assist reads that as a real slowdown, so it closes only part of the gap.

when they step aside¶

Both cut out fast and stay off for 3 s after the cause clears for: a collision warning, a predicted hard brake, a forced slowdown (for example when you are not responding), your foot on either pedal, or a lane change.

• Speed Assist also stands down whenever a car is ahead.
• Lead Follow Assist also stands down when the lead changes (a cut-in or a new car), is below 80% confidence, is slower than about 11 mph (18 km/h), brakes, or is forecast to slow by 1 m/s within 3 s. It also waits out a stop or slowdown in the model's plan, the model braking, or a bend over 1.0 m/s², then builds back up over 2 s.

requirements and settings¶

You need experimental speed control (Alpha Longitudinal) and Experimental Mode on, and Dynamic Experimental Control off: while it is on, both assists do nothing and their switches are greyed out.

Open Settings → Cruise. On comma 4 the switches are under alpha longitudinal; on comma 3X they are at the top of Cruise.

• Experimental Mode Speed Assist (speed assist on comma 4).
• Experimental Mode Lead Follow Assist (lead follow assist on comma 4).
• Driving Personality: sets the following distance and Lead Follow Assist's cap.

I tested both assists in simulation against recorded drives. On-road feedback is welcome.