The feature toggle icons found on various level elements can be hidden to reduce visual clutter.
This affects traffic speed limit values.
You’ll probably want to have this on. As you modify your road network, auto-regeneration will keep NPC traffic properly updated. Disable this to manually tweak traffic properties, such as limiting lanes to specific NPC types.
Road lane configurations can sometimes become invalid if traffic is set to drive both ways on a single lane. This setting will help in locating such issues.
Just leave this to “Rounded”, the setting affects road curves, and it’s only visible for legacy compatibility reasons.