Traffic Congestion and Headway Conflict

TAILGATING (LOW VEHICLE HEADWAY TIME) especially at merges, is a major avoidable driver cause of congestion and danger on expressways
(controlled access highway, freeway, motorway, autobahn).

SLOWPOKING (HIGH VEHICLE HEADWAY TIME) on a busy expressway, can waste scarce traffic flow capacity and add to congestion and danger (causing turbulence by forcing others to brake, change lanes).

HEADWAY = TIME SPAN STARTING NOW FOR THE VEHICLE FRONT TO GET AT SPEED NOW TO WHERE THE NEXT VEHICLE FRONT IS AT NOW.

1.8 SECOND HEADWAYS (STANDARD SAFE MINIMUM) give time enough to expressway drivers to react smoothly and safely as traffic changes, avoid causing jam / crash with sudden actions forced by urgent event.

THEIR VEHICLE HEADWAY IS THE KEY TEAM FACTOR EVERY DRIVER CAN USE TO ASSIST OPTIMUM EXPRESSWAY TRAFFIC OPERATION.

Headway conflict occurs, whenever vehicle headway times are too low (in any traffic) and / or too high (in busy traffic), for safe efficient flow.

Merging (e.g. on-ramp, routes join, lane change / drop) forces down headways -- to especially congesting and dangerous lows, if upstream drivers already tailgate (headways too low) before their merge.

Traffic overload, seen as another big cause of congestion, is headways too low (flows too high) of vehicles entering the expressway network.

ETO ENDS HEADWAY CONFLICT -- ROOT CAUSE OF CONGESTION.

Vehicle Headway and Traffic Safety

Headway links speed and distance in a continual **safety** time metric: the **current** travel time of the moving vehicle front, to get to the **current** location of a key moving point ahead: the front of the **next vehicle** ahead.

       DISTANCE         DISTANCE       
HEADWAY = ------------ = ----------------- = TIME
             SPEED        DISTANCE / TIME        

     To INcrease your headway time => increase gap |  reduce speed.
     To DEcrease your headway time =>  reduce gap  | increase speed.

Gap = distance from vehicle front to the back of the next vehicle ahead.

UNDERSTAND HEADWAY SAFETY
AS TIME THE DRIVER HAS
TO HANDLE WHATEVER HAPPENS,
 
UP TO THE PLACE AHEAD
WHERE THE NEXT VEHICLE FRONT IS NOW.
 
 YOU ARE NOT ALONE !! 
 
WHEN YOU CHANGE YOUR HEADWAY YOU
ALSO AFFECT THE HEADWAY OF
THE VEHICLE FOLLOWING YOU,
 
JUST AS THE DRIVER AHEAD OF YOU
CAN AFFECT YOUR HEADWAY WITH THEIRS.

Smart drivers cooperate and team with fast safe smooth headways.

ETO COACHES YOUR HEADWAY TEAM WITH "SMART ROAD" SIGNALS.

Vehicle Headway and Traffic Flow

Imagine you stand beside a busy highway. Count vehicles passing you in one lane. In one hour, your vehicle count is an average traffic flow rate in that lane at that location (vehicles per lane.hour).

Average vehicle headways determine average traffic flow rates. Traffic using 1.8 second average headways, flows at average 2000 vehicles per lane.hour (3600 seconds per lane.hour / 1.8 seconds per vehicle).

2000 vehicles per lane.hour is an expressway standard safe maximum traffic flow capacity, corresponding to the 1.8 seconds standard safe minimum vehicle headway (1.8s = safety vs efficiency balance point).

Tailgating (headways less than e.g. 1.8 seconds), actually is correct to increase expressway traffic flow. Unfortunately tailgating can be very unsafe and also usually soon shocks traffic flow into congestion.

UNDERSTAND HEADWAY COST
AS AMOUNT OF
LANE TRAFFIC FLOW CAPACITY
USED BY THE VEHICLE NOW.
 
EXPRESSWAY DRIVERS FACE
A CLASSIC SAFETY VS EFFICIENCY
(TIME VS FLOW) HEADWAY CHOICE.
 
 HEADWAYS SOAR TO 12+ SECONDS !! 
 
IN SEVERE CONGESTION,
CRUSHING FLOW DOWN
 
 **BY 85% OR MORE** 
 
TO 300 VEHICLES PER LANE.HOUR OR LESS
(3600 SECS PER LANE.HOUR / 12 SECS PER VEHICLE.)

THIS HUGE WASTE OF 85% OR MORE OF TRAFFIC FLOW CAPACITY IS ENTIRELY CAUSED BY DRIVERS THEMSELVES. THEIR EASY FIX IS TO USE APPROPRIATE (ETO) HEADWAYS THAT BANISH CONGESTION.

Traffic Flow, Vehicle Speed and The BTO

Society, for SAFE EFFICIENT use of expressways, chooses 1.8 seconds as (minimum) safe vehicle headway, accepting a (maximum) high flow rate of 2000 vehicles per lane.hour.

To keep an expressway busy with SAFE EFFICIENT traffic, ETO could pack many vehicles close e.g. 12.5 m (41 ft) between front bumpers, and use low speeds e.g. 25 kph (16 mph), for 1.8 second headways.

But society's individual members want quick trips. Few would be happy at 25 kph (16 mph), and many would use unsafe excessive speeds.

So society sets a safe (maximum) high speed of e.g. 100 kph (60 mph),
and allows a lower (minimum) medium speed of e.g. 90 kph (55 mph).

ETO coaches drivers, to use speeds of e.g. 90 - 100 kph (55 - 60 mph),
with more space e.g. 45 - 50 m (148 - 164 ft) between front bumpers,
to maintain 1.8 second headways:

   traffic flow together with traffic speed indicate the busy traffic optic

        tailgating  or  safe & efficient  or  slowpoking  or  congestion