Driving cars these days is so unpleasant and stressful its hardly surprising that some drivers can't resist having a go at anyone. Many car drivers have developed a laager mentality, with increasing levels of congestion, petrol prices, and a feeding frenzy of parking clampers, speed trappers etc.. In Portsmouth an area of largely unused parking space was turned into a segregated cycle path. You cannot imagine the bile coming out over this terrible imposition on the beleaguered car driver.
Virtually all space on a road is accessible to car drivers. Even excluding motorways, there are many stretches of road that are virtually inaccessible to cyclists due to the design of the roads/junctions creating high speed traffic. Cycle lanes do little for cyclists, except promote the idea that cyclists only belong at the extremes of the road, in regions that car drivers can use any time they feel the need (to park or when over taking).
Our roads remain very safe (for drivers) but the number of pedestrians, cyclists etc. killed or seriously injured continues to remain much higher. Car design makes it safer (for drivers) and easier for drivers to go at higher speeds. Its really cars that need segregating, not cyclists.
Personally I'd favour taking 20% of all road space and converting it into segregated cycle lanes (roughly a dutch/danish model). In any case most roads are currently only operating at 80% or less of the available width due to onroad parking. Probably most drivers would actually benefit by lower levels of congestion since many of the single occupant/short trip journeys taken by car, and might even find driving a bit less stressful than it is at the moment.