On the 10th of September, several DC cops assigned to or othewiseescorting the monthly Bike Party drive their cars in ways that made someof the riders feel they were being put as risk for a collision. Theymuscled their cars directly into the packs of riders, followed ridersahead of them too closely, and as a result had to make sudden stops thatput riders behind them at risk of ramming the police cruisers if theycould not stop quickly.The most dangerous conditions occurred on two lane roads, where police cars were able to block the entire lane going the direction of the ride. On wider roads the intrusion of the police cars was less dangerous because there was more room to get around them when they stopped too quickly, and may not have followed riders as closely when they were less densely packed. As usual there were over 600 riders in the Bike Party, I do not know if this was just cops unused to driving in such close proximity to cyclists or an organized plan to harass the rides so as to reduce turnout.There were also strong efforts by these same police to break up the large packs of riders when traffic lights changed. The lead elements of these rides only cross intersections on green, but the length of the ride often causes lights to change before all riders can pass. Serious police aggression such as the throwing open of doors or attempts to tackle riders did not occur, either not being intended in the first place or just because police were outnumbered nearly 100-1. Still, the moves by police near traffic lights reminded me of police aggression at intersections during the Oct 2002 IMF Critical Mass ride that later ended up at Pershing Park.As this aggression angered riders some began to respond by pushing through the intersections, neutralizing some of the police efforts to divide the ride up at intersections with changing lights. As the ride continued the police cruisers found themselves at the very end of the ride shortly before 9PM, out of most rider's hair. I do not know if this situation later escalated because I had to break off to cover the antiwar protest that met Obama's Iraq speech at 9PM the same night.If even one bicyclist is injured as a result of careless or aggressive driving by police, the city could face significant legal judgements in court. If the police insist on trying to control the Bike Parties, they should at least learn to drive their cars in a way that does not create a risk of dangerous car-bike collisions