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From page 183... ... 181 B METHODOLOGICAL DETAILS INTRODUCTION This appendix augments Chapter 3 by providing additional details about how to analyze travel time reliability for segments, routes, and networks. Except for the next section on the processing steps, which is new, the appendix follows the structure of Chapter 3 to facilitate cross referencing and cross checking. Read the entire page →
From page 184... ... 182 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY The segment travel times and rates can then be combined to develop route-level travel times and rates. The combination process is not trivial because strong correlations exist among the times observed on adjacent segments, but it is possible to generate these multisegment density functions. Read the entire page →
From page 185... ... 183 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY From a travel time reliability perspective, the attributes of the four data feeds are as follows: 1. Spot speeds (spot travel rates) Read the entire page →
From page 186... ... 184 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY travel times can be observed but vehicles cannot be tracked from one segment to the next because their IDs are suppressed. The L02 research team encountered this type of data set in one of the case studies. Read the entire page →
From page 187... ... 185 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY Highlights from Table B.1 include the following: • It is important to develop passage times (time stamps) for data Types 3 and 4. Read the entire page →
From page 188... ... 186 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY On rare occasions when a large number of AVI- or AVL-equipped vehicles make the same trip at the same time (e.g., between interchanges on a freeway) , the individual vehicle PDFs can be observed directly. Read the entire page →
From page 189... ... 187 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY very closely spaced. The influence of multiple paths and stops needs to be removed by truncation (filtering) Read the entire page →
From page 190... ... 188 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY 1. The users (e.g., travelers, vehicles, packages, trucks) Read the entire page →
From page 191... ... 189 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY SEGMENT TRAVEL TIME CALCULATIONS Segment travel time computations lie at the heart of travel time reliability. It is critical that high-quality travel times are developed from whatever data sources are available. Read the entire page →
From page 192... ... 190 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY A second option also works well. Equation B.2 uses two parameters α and β to combine the spot rates: s 1 2α βτ = τ + τ (B.2) Read the entire page →
From page 193... ... 191 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY Bluetooth data were available for 4 days in January 2011: Thursday, January 13; Thursday, January 20; Saturday, January 22; and Monday, January 24. One or more periods of congested operation occurred during each of these days, as shown by Table B.2. Read the entire page →
From page 194... ... 192 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY Figure B.3. Off-peak travel rates measured by Bluetooth sensors for the Berkeley Highway Laboratory. Read the entire page →
From page 195... ... 193 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY 0% 5% 10% 15% 20% 25% 0 50 100 150 200 250 300 350 400 450 Pe rc en ta ge o f V al ue s i n 50 s ec R an ge (≈ P DF ) Travel Rate (sec/mi) Read the entire page →
From page 196... ... 194 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY ROUTE TRAVEL TIME CALCULATIONS The material in this section of Chapter 3 is essentially complete. Described there are procedures for developing average route travel times and distributions of individual vehicle travel times based on (a) Read the entire page →
From page 197... ... 195 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY stations is 39, 9, 10, and 11. Travel times are TT3909, TT0910, and TT1011. Read the entire page →
From page 198... ... 196 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY Developing Incidence Matrices One way to address the correlation among segment travel times is to develop incidence matrices. Read the entire page →
From page 199... ... 197 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY Developing PDFs for Average Travel Times or Rates Agencies are often concerned with how their facilities are performing across the year (or some other time frame) given the vagaries of the load conditions to which they are exposed, such as incidents, inclement weather, and unexpected demand conditions. Read the entire page →
From page 200... ... 198 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY the detectors in the field as opposed to being imputed. In addition, to the extent possible, the external factors that might have influenced freeway performance (e.g., weather incidents) Read the entire page →
From page 201... ... 199 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 7 9 11 13 15 17 19 21 23 25 Cu m ul ati ve P ro ba bi lit y Travel Time (min) AM Peak Travel Time CDFs Weather Incident Normal All Figure B.8. Read the entire page →
From page 202... ... 200 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY CONSIDERATIONS FOR TRANSIT Most of the discussion in this appendix has focused on vehicle (effectively auto) travel times. Read the entire page →
From page 203... ... 201 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY Because carriers rarely share their package-level information except with the stakeholders (the shipper and receiver) who have a need-to-know interest, providing reliable service to freight carriers becomes functionally similar to dealing with reliable travel times for autos. Read the entire page →
From page 204... ... 202 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY Figure B.9. Analysis flowchart for transit trips involving transfers. Read the entire page →
From page 205... ... 203 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY of departing early (earlier than the scheduled departure time) and a much larger probability of departing late. Read the entire page →
From page 206... ... 204 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY destination Δt11 = 190, and arrives at the destination at t12 = t10 + Δt11 = 1,870 + 190 = 2,060 with an arrival relative to the scheduled arrival time of Δt12 = −10 (10 seconds early) and an overall travel time of tt = t12 − t0 = 2,060 − (−120) Read the entire page →
From page 207... ... 205 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY scheduled departure time) Read the entire page →
From page 208... ... 206 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY every 0.5 miles. This is a bit dense, but typical. Read the entire page →
From page 209... ... 207 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY 0 5 10 15 20 25 30 35 40 MP 21:7MP 00:6MP 84:4MP 63:3MP 42:2 Tr av el T im e (m in ) Time of Day Individual Vehicle Travel Times / I-5 Southbound Figure B.11. Read the entire page →
From page 210... ... 208 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY A formal technique to estimate minimum sensor spacing and sampling intervals was developed as part of the project and is included in the final report. The conclusions from that work are as follows: • Temporal sampling intervals in the range of 1 to 5 minutes should be adequate for most situations in which both recurring and nonrecurring events occur, although 30 seconds is somewhat better. Read the entire page →

From page 183...

... 181 B METHODOLOGICAL DETAILS INTRODUCTION This appendix augments Chapter 3 by providing additional details about how to analyze travel time reliability for segments, routes, and networks. Except for the next section on the processing steps, which is new, the appendix follows the structure of Chapter 3 to facilitate cross referencing and cross checking.