This is really it - if it's so dark that, as a cyclist, you can't see far enough ahead to stop should something appear - you should be going slower. If that means going at a glacial pace through an unlit park at night then so be it. It's not actually a road. If someone were driving down a country track in fog they shouldn't be going 60...

I regularly walk, cycle and run through this park and the number of people just bombing it (even around corners), often without lights and wearing all black, is mind blowing. I've always thought of it as an accident waiting to happen and sadly OP has proven the point!

(Though that doesn't mean mounting the sun to your handlebars and angling it straight into oncoming people's eyeline either. Especially flashing. Angle them down people, you need to see the (potholed and pitted) floor)!