Are you too short to hold on to BART top rails?

Simple, elegant, functional, rugged. Made of plush heavy duty nylon webbing, aircraft grade aluminum, and high-friction neoprene for a no-slip grip on the bar. Washable.

Includes an integral acetal D-ring to add options like the TranStrap Pass Holder and TranStrap Reader Sling. Fits all trains, subways, and buses. Measures 1.5" by 13" tall fully extended, but folds to cellphone size to stow easily in your pocket, purse, briefcase, or pack.
From the FAQ on site
Does the TranStrap really work?
In short (no pun intended): Yes. We tested and tinkered with TranStrap until it not only worked but it worked extremely well. We tested with men and women, short and tall, thin and heavy, on subways and buses. The design, materials, and method of assembly produce a set of patented proprietary features that cause it to perform beyond expectation.

Is it as safe as holding on?
Let's be real clear about the safety question: TranStrap is not a life safety device. It will not protect you from a radical, sudden stop on a train or bus. Then again, nothing short of the Michelin Man suit would protect you. TranStrap provides a more comfortable and hygienic transit experience under normal conditions. Please err on the side of conservative good judgment in deciding when and how you use the TranStrap.
How short can you be and still use the TranStrap?
We don't have hard figures on this but we know that if you can touch the bottom of the bar with the tips of your fingers with your feet flat on the floor, you can use the TranStrap. This is because the top 4" of the TranStrap is rigid enough to give you a 4" advantage and that's more than enough to get it on and off the bar with one hand. If you can't touch the bar at all, it probably won't work for you.