level crossing lghts only Bunza modified

/* Grade Crossing LED's triggered by IR Sensors
Adapted from Geoff Bunza's sketch Not using the Servo actuated Gate Arms
Modified by Gary Granai 25 September, 2020
https://steamtraininfo.com/arduino-projects

*/
int sensor1 = 5; // IR sensor==Pin goes LOW when train detected
int sensor2 = 6; // IR sensor==Pin goes LOW when train detected
int led1 = 10; // Led 1 pin alternating flasher
int led2 = 11; // Led 2 pin alternating flasher
int led3 = 14; // Led 3 pin alternating flasher
int led4 = 15; // Led 4 pin alternating flasher
int entering_sensor = 5; // which sensor was triggered first
int leaving_sensor = 6; // which sensor shows train leaving
int sequence_started = 0; // this says if the crossing is active
int flash_state = 0; // variable for function flash_leds()
long flash_time = 0; // variable for function flash_leds()
long flash_interval = 900; // time in milliseconds between alternating flashes
int sensor_count = 0; // declare variable for while statement

void setup() {

pinMode(sensor1, INPUT); // sensor1 is an INPUT
pinMode(sensor2, INPUT); // sensor2 is an INPUT
pinMode(led1, OUTPUT); // led1 on pin 10 is an OUTPUT
pinMode(led2, OUTPUT); // led2 on pin 11 is an OUTPUT
pinMode(led3, OUTPUT); // led3 on pin 14 is an OUTPUT
pinMode(led4, OUTPUT); // led4 on pin 15 is an OUTPUT
digitalWrite(led1, LOW); // Start with flashers off
digitalWrite(led2, LOW); // Start with flashers off
digitalWrite(led3, LOW); // Start with flashers off
digitalWrite(led4, LOW); // Start with flashers off
flash_time = millis(); // for function flash_leds()
}

void loop() {
// The two if statements defines which sensor is which and
// changes sequesnc_started from FALSE to TRUE then starts
// the leds flashing
if ((digitalRead (sensor1) == LOW) && (sequence_started == 0)) {
sequence_started = 1;
leaving_sensor = sensor2;
flash_leds();
}
if ((digitalRead (sensor2) == LOW) && (sequence_started == 0)) {
sequence_started = 1;
leaving_sensor = sensor1;
flash_leds();
}
// First if== sequence started and continue flashing leds
// Next if== train is leaving the crossing
if (sequence_started) flash_leds();
if ((digitalRead(leaving_sensor) == LOW) && (sequence_started == 1)) {

// as long as the leaving sensor is active the train is still in the crossing
// while checks if train is gone yet
while (sequence_started == 1) {
sensor_count = 0;
for (int i = 1; i < 40; i++) {
if (digitalRead(leaving_sensor) == LOW) sensor_count++;
delay (30);
flash_leds();
}
if (sensor_count == 0) sequence_started = 0;
flash_leds();
}
// At this point train is no longer over the leaving sensor
digitalWrite(led1, LOW); // Turn OFF led
digitalWrite(led2, LOW); // Turn OFF led
digitalWrite(led3, LOW); // Turn OFF led
digitalWrite(led4, LOW); // Turn OFF led
}
}

void flash_leds() {
if (flash_time > millis()) return;
flash_state = ~flash_state;
digitalWrite(led1, flash_state);
digitalWrite(led2, ~flash_state);
digitalWrite(led3, flash_state);
digitalWrite(led4, ~flash_state);
flash_time = millis() + flash_interval;
}