The "blinkey" kit only has one "flaw"--- the leds will not be on for the same time-- the circuit as built will have one led on for 1/3 the other on for 2/3 of a cycle. Real crossing warning lights use a 50% duty cycle. To fix this circuit to generate a 50% duty cycle, all that needs to be added is a 1N4148/1N914 diode across the R2 resistor. The cathode(the end marked with a band) of the diode must be connected to the cap/resistor junction.
The Diode in effect shorts out the R2 resistor during the IC's charge time, and as long as the R1 and R2 are the same value, you will get a 50% duty cycle.