Impact Analysis of Roadway Surface and Vehicle Conditions on Fleet Formation for Connected and Automated Vehicles

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Impact Analysis of Roadway Surface and Vehicle Conditions on Fleet Formation for Connected and Automated Vehicles

by

Dr. Ping Yi, P.E.

The University of Akron

April 12-13, 2022

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Signiﬁcantly impacting the evolution of next- generation Transportation systems 2

Outline

• Background

• Objectives

• Research Focus

(1) Issue 1: understanding of the impact of roadway surface, vehicle, and other environmental factors on skid resistance

•

pavement friction behavior for in-service roads

•

other vehicle and tire conditions on skid resistance

(2) Issue 2: time dependent dynamic fleet model

•

introducing base model

•

impact analysis due to disturbances

• Conclusion and Further Work

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 Over 6.7 million crashes reported by Police in 2018. Nearly 37,000 people died in 2018.

 Over 52,000 vehicles involved in fatal crashes in 2018.

Background: Crash Statistics

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Background: Crash Economics

• Economic cost of all motor vehicle traffic crashes in the U.S in 2010 was estimated $242 billion, as tangible losses.

 When intangible costs such as the

quality of life valuations are

considered, the total cost of societal

harm due to traffic crashes in 2010

was estimated $836 billion.

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How to set car following spacing in a CAV Fleet?

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Objective

To investigate the impact of roadway, vehicle,

and other environmental conditions on safe

formation of CAV fleets.

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Issue 1 – Roadway Surface Skid Resistance

• Roadway surface must have an appropriate level of pavement friction to be able to keep vehicles safely in the lane;

 Poor pavement conditions (such as worn surface in wet condition) is one of the major contributing factors in roadway departure crashes;

• FHWA indicates that about 70 percent of wet pavement related crashes may be prevented by improved pavement friction.

It is understood that…

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Roadway Surface Friction

HOW TO assess roadway friction-related safety ?

1. field measurement and monitoring

- expensive and time consuming

2. modeling and estimation

- laboratory test + field sampling

- computer modeling and validation

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Polishing Susceptibility

 Laboratory work to prescreen polishing susceptibility

– short and simple laboratory tests

e.g., versatility of testing different HMA specimens

4”

6”

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Short-term field sampling at limited locations Sampling

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 Friction is affected by two opposing actions in real world :

– Surface polishing due to traffic load

– Roughening action due to rainfall and environmental factors

Field Sampling

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• According to FHWA and NTSB a significant proportion of traffic crashes directly or indirectly related to inadequate stopping sight distance.

If we isolate surface friction as a focus in the analysis…

Implication of Friction on Stopping Sight Distance

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• A commonly used formula to derive stopping sight distance (SSD) is based on well-established fundamental principles of mechanics.

• SSD consist of two parts:

 Reaction distance due to human driver, 𝑉𝑉 𝑡𝑡

_𝑟𝑟

 Braking distance due to mechanical process, 𝐷𝐷

_𝐵𝐵

𝑺𝑺𝑺𝑺𝑺𝑺 = 𝑽𝑽 𝒕𝒕 _𝒓𝒓 + 𝑺𝑺 _𝑩𝑩

𝑺𝑺 _𝑩𝑩 = 𝟐𝟐𝟐𝟐(𝝁𝝁+𝑮𝑮) ^𝑽𝑽

^𝟐𝟐

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 𝐷𝐷 _𝐵𝐵 is the focus of discussion in the CAV environment

 𝐷𝐷 _𝐵𝐵 can be measured based on AASHTO recommended Coefficient of Friction. For example,

AASHTO Guideline

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 NCHRP report 400

 Instead of specifying the coefficient of friction AASHTO recommend using the following equation

𝐷𝐷 _𝐵𝐵 = _{2(𝑎𝑎+𝑔𝑔𝑔𝑔)} ^𝑉𝑉

²

 𝑎𝑎 is the recommended deceleration rate, 3.4 m/s

²

 𝑉𝑉 is design speed (not vehicle running speed)

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Significantly impacting the evolution of next- generation Transportation systems 32.635

47.885

0 10 20 30 40 50 60

DB, (M)

Consumer Report Braking Distance vs. AASHTO

6

Braking Distance

32.635

47.885

114.7

0 20 40 60 80 100 120 140

DB, (M)

Consumer Report Braking Distance vs. AASHTO

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Different vehicles at same speed on same road may require

different Braking Distances (D _B ).

10.5

14.5 12.5

21.6

28.7

5.0 10.0 15.0 20.0 25.0 30.0 35.0

DB(M)

Emergency Braking Distance (D

_B

) at 50 (Km/h)

Badly Worn Tire

So Pavement Friction is Not the Only major factor to consider for a

safe stop.

Braking Distance

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Significantly impacting the evolution of next- generation Transportation systems 8

• The traditional friction theory, which is accepted now, is based on metallic friction theory: µ= _𝑊𝑊 ^𝐹𝐹

 Traditional friction law doesn’t work as desired for rubber.

Adhesion vs Hysteresis

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 Road surface conditions are different because construction materials vary from situation to another. Thus, tire-pavement friction varies with location and time.

 Tire tread and quality may vary from one vehicle from another

 Vehicle braking effect and stability systems may also function

differently

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Significantly impacting the evolution of next- generation Transportation systems

Road &

Pavement Factors

Braking Distance

Vehicles Factors

14 Issue 2: Time-dependent Fleet Model

1. Other factors also affect the roadway resistance and safe stopping of a vehicle.

2. A passive (pre-determined) system won’t be able to truthfully and timely describe

the impact on CAV operation.

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Driving Force ∝ Power Produced at Engine

Power Produced at Engine ∝ Engine Load

Total Resistance ∝ Engine Load, Weight, Speed

Total Resistance < Driving Force

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Resistance and Engine Power

R

_T

=R

_R

+ R

_C

+R

_G

+R

_air

F

_D

>R

_T

Driving Power P

_D

=λP P

_D

= VF

_D

P

_D

∝ R

_T

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Resistance and Engine Power

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Braking Process

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𝑚𝑚 ̈𝑥𝑥 = F - 𝑚𝑚 𝑔𝑔 sin 𝜃𝜃 - ₂ ̇𝑥𝑥 - 𝑑𝑑 _𝑚𝑚 ⟶ (1)

• The engine of vehicle is modeled as :

̇𝐹𝐹̇= −𝜏𝜏 𝐹𝐹 + 𝑢𝑢 ⟶ (2)

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Platoon Formation

•Number of vehicles, N

•All vehicles with the same speed, v _d

•A desired minimum distance, L, between two successive vehicles.

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String Stability:

It is required to ensure that the spacing errors do not amplify upstream from

vehicle to vehicle in a platoon.

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𝑅𝑅 _𝑖𝑖 𝑠𝑠 = 𝑒𝑒 _𝑖𝑖 𝑠𝑠 𝑒𝑒 _𝑖𝑖−1 𝑠𝑠

||𝑅𝑅 _𝑖𝑖 𝑠𝑠 || _∞ ≤ 1 and 𝑅𝑅 _𝑖𝑖 𝑡𝑡 > 0 𝑖𝑖 = 1,2 … . 𝑁𝑁 A sufficient condition for string stability is that the spacing error must not increase as it propagates through the platoon.

The spacing error propagation transfer function is defined by:

String/Platoon Stability

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𝑹𝑹 _𝒊𝒊 𝒔𝒔 = 𝒄𝒄 _𝒗𝒗 𝑺𝑺 + 𝒄𝒄 _𝒑𝒑

𝑺𝑺 ^𝟑𝟑 + 𝒄𝒄 _𝒂𝒂 𝑺𝑺 ^𝟐𝟐 + 𝒄𝒄 _𝒗𝒗 + 𝒄𝒄 _𝒑𝒑 𝒉𝒉 𝑺𝑺 + 𝒄𝒄

𝑅𝑅 _𝑖𝑖 𝑠𝑠 = 𝑒𝑒 _𝑖𝑖 𝑠𝑠 𝑒𝑒 _𝑖𝑖−1 𝑠𝑠

𝒆𝒆 _𝒊𝒊 𝒔𝒔 𝑺𝑺 ^𝟑𝟑 + 𝒄𝒄 _𝒂𝒂 𝑺𝑺 ^𝟐𝟐 + 𝑺𝑺 𝒄𝒄 _𝒗𝒗 + 𝒄𝒄 _𝒑𝒑 𝒉𝒉 + 𝒄𝒄 _𝒑𝒑 = 𝒆𝒆 _{𝒊𝒊−𝟏𝟏} 𝒔𝒔 𝒄𝒄 _𝒗𝒗 𝑺𝑺 + 𝒄𝒄

Transfer Function

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Performance of the Transfer Function (𝑮𝑮 _𝒊𝒊 𝒔𝒔 )

• Stability of the System (Poles)

• Performance Measures/Parameters

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Leader Block

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Tuning of the Parameters Trial & Error Method

• Testing with different parameter combinations

• Keeping string stability requirements when deciding on parameter values

• Evaluating testing results by looking at the risetime and settling time

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Performance After Disturbance

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Impact Analysis of Roadway Surface and Vehicle Conditions on Fleet Formation for Connected and Automated Vehicles

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