Traffic Light Control using Reinforcement Learning

Final Presentation
Traffic Light Control
Using Reinforcement Learning
Daniel Goldberg
Andrew Elstein
The Problem
• Traffic congestion is estimated to cost Americans $121
billion in lost productivity fuel, and other costs.
• Traffic Lights are imperfect and contribute to this
Usually statically controlled
• A better method of controlling them can reduce waiting
times significantly
• Implement a
Learning” (RL) algorithm
to control traffic lights
• Create a simulation of
traffic to tweak and test
traffic light optimizations
• If minor adjustments were
made to the algorithm, it
could operate within
existing infrastructure
• Optimally, a camera system
and would be added
Insert picture of visualization
Simulation Structure
To build the simulation we created the follow Data Structures:
Position, Destination, Velocity, Map, Color
ars Struct
• Lanes
Individual Cells
• Intersection location matrix
In total, the simulation is coded in
• Position, Traffic Lights
MATLAB with 3100 lines of code
Simulation Dynamics
Cars are spawned randomly
They follow an randomly generated path to destination
Cars follow normal traffic rules
Road Cells are discretized to easily simulate traffic, only one car
can exist in each road cell. Cars move ahead one or two cells in
each time-step, depending on the car's max velocity and
whether there is an open spot.
Reinforcement Learning
Weiring - Multi-Agent Reinforcement Learning for Traffic Light
It introduced an objective function to minimize or maximize a
goal value
 , ,  , ,  ′ , ′
 , ,  ,  =
∗ ( ,  ,  ′ , ′
( ′ ,′ )
 , , 
 | , ,   , ,  , 

 ,  ,  ′ , ′
 ,  = [ ′ , ′ ]
 ,  ≠ [ ′ , ′ ]
= traffic light
= current position
= destination
= light decision
 = discounting constant
‘ = next
+ (  ′ , ′ ,  ))
Reinforcement Learning Theory
Coordinating a system of lights to respond to current conditions
can reap exceptional benefit
The theory cleverly merges probability, game theory and machine
learning to efficiently control traffic
In our case, the expected value of each of a light’s possible states
are calculated
With this value function a game is played to maximize it, in turn
minimizing waiting time
Wrote a script to compare the smart algorithm to static On-Off-On-Off
Our algorithm reduced average waiting time—and thus traveling time—
for a system with any number of cars
Travelling time for our implementation was reduced by an average of
10%. There was a 15% reduction for sparse traffic systems from a static
control, but only a 3% decrease for heavy congestion.
Results cont.
• Fairness-weighted objective:
ω = weighting constant
t = current time
ti = time of arrival for car i
If F(t) > 1, cars on road 1 get to go
If F(t) < 1, cars on road 2 get to go
Further Extensions
• Car Path optimization and rerouting
• Model expansion to traverse an entire city
• Inter-traffic-light communication
• Retesting with increased computational resources for
modeling accuracy and robustness
RL In the News
• Samah El-Tantawy, 2012 PhD recipient from the University of
Toronto, won the 2013 IEEE best dissertation award for her
research in RL.
• Her RL traffic model showed reduced rush-hour travel times
by as much as 26 percent and is working on monetizing her
research with small MARLIN-ATSC (Multi-agent
Reinforcement Learning for Integrated Network of Adaptive
Traffic Signal Controllers) computers.
• Difficult to understand data structures and how they
would interact
Object Oriented Approach vs. MATLAB’s index-based structures
• Understand how cars would interact with each other
• Understanding RL algorithm
• Adapting our model to use RL algorithm
• Limited computational resources

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