About

Alec Rhodes is an assistant professor of sociology at Purdue University in the College of Liberal Arts. He is an economic sociologist who studies the causes and consequences of inequality and financial insecurity. His research employs political economy, demographic, and spatial perspectives to explore questions related to inequality, poverty, and mobility. He is particularly interested in how inequalities accumulate over the life course and across different market contexts, as well as the potential for institutions and policy to mitigate inequalities and hardships. His recent work focuses on labor market institutions and the distribution of resources and opportunities across careers and places in the United States. Additionally, he examines the relationships between social policy and credit use among low-income populations, along with the consequences of debt and financial hardship for life chances. His methodological approach involves using survey and administrative data combined with advanced quantitative methods, including longitudinal data analysis and causal modeling. Prior to his position at Purdue, Alec completed a postdoctoral fellowship at the University of Wisconsin-Madison's Institute for Research on Poverty. He earned his PhD from Ohio State University and his BA from Hobart and William Smith Colleges.

Research topics

• Transport engineering
• Engineering
• Computer science
• Environmental science
• Forensic engineering

Selected publications

• Real-Time Adaptive Traffic Control System Evaluation Superstition Springs Mall Area in Mesa, Arizona

  2012-01-01

  articleSenior author

  The City of Mesa, AZ installed a SCATS (Sydney Coordinated Adaptive Traffic System) in early 2011 controlling 18 signalized intersections near Superstition Springs Mall, an area with significant traffic volume fluctuations. This paper compares the City's time-of-day (TOD) traffic signal operation with SCATS operation for both low season (summer) and high season (winter) volumes. Both intersection turning movement counts and midblock traffic volumes were collected. Travel times (both Bluetooth re-identification and GPS) as well as minor street queue and delay data were collected for both seasonal periods in consecutive weeks, with one week being SCATS operation and the next week being TOD operation (i.e. with SCATS turned off). The Bluetooth travel times were obtained by matching of Bluetooth MAC addresses at upstream and downstream locations with the travel times between them determined. This paper presents before and after results including average travel time and speed, number of stops, average intersection delay and minor street delay for TOD and traffic adaptive operation during both seasonal periods. A statistical comparison was made to test for significant differences in measures of effectiveness. In an attempt to account for the effect of non-recurring events on traffic operations, traffic incidents, special events and weather-related events were compiled for the study area during the study periods and considered in the comparison.

  Publisher

• Operational Performance Comparison of Video Detection Systems

  ITE 2007 Annual Meeting and ExhibitInstitute of Transportation Engineers (ITE) · 2007-12-01 · 16 citations

  article1st authorCorresponding

  This paper describes how video detection has become increasingly popular for presence detection at signalized intersections because of its versatility and ease of installation. However, several reports have documented performance problems in specific systems. The performance of three different commercially available video detection systems are studied in this paper. The systems were tested in May and September 2005 for presence detection accuracy. Prior to the May 2005 test, a representative from each vendor configured the video detection zones to match the loop detection zones as closely as possible. The outputs from the loop detection for the through-right and left-turn lane groups were compared with the corresponding output from each of the video detection systems. Whenever there was a discrepancy between the loop and video, a digital video was observed in order to determine the cause of the discrepancy. Missed calls and false calls were categorized for each system and the errors were also categorized according to the impact that they would have on signal operations. During a 24 hour test on two separate days, the number of missed detections longer than 5 seconds ranged from 9 to 147, and the number of false calls longer than 5 seconds ranged from 14 to 159. The loop detectors had one false call longer than 5 seconds and one missed call longer than five seconds during both tests. Although technology has advanced in the two years since this test was completed, the results documented in this paper apply to a large number of installations that have not been upgraded since the fall of 2005. This paper further highlights the importance of developing rigorous detection performance specifications so agencies can make informed decision about the relative advantages and disadvantages of alternative detection technology.

  Publisher

• Consistency of Video Detection Activation and Deactivation Times between Day and Night Periods

  Journal of Transportation Engineering · 2007-08-17 · 25 citations

  article1st author

  Video detection has become an increasingly popular technology for vehicle detection at signalized intersections. Among the potential disadvantages of this technology is the tendency of video detectors to activate early at night due to headlight reflection on the pavement. This early activation results in a dramatic increase in the length of the effective vehicle detection zone. This observed variation in the effective length of the vehicle detection zone that varies by ambient lighting condition and camera placement presents a very serious impediment for traffic engineers to design vehicle extension intervals that operate consistently during day, night, and transition periods. Further, the stochastic variation in the length of the vehicle detection zone length has the potential to create driver expectancy issues. Tables are included that report the observed average and range of detection zone length variations for 16 observed video cameras that were extensively calibrated by the manufacturer at the test site. The paper concludes by recommending near-side placement of video detection devices to reduce the stochastic variation in detection zone length.

  PublisherDOI

• Evaluation of Stop Bar Video Detection Accuracy at Signalized Intersections

  2006-01-01 · 16 citations

  reportOpen access1st authorCorresponding

  Many agencies nationwide have adopted video vehicle detection technology as an alternative to inductive loops. While many product evaluations have been performed, the majority of these evaluations have concentrated on freeway applications where speed and volume were the primary evaluation criteria. At an actuated intersection, the metrics of speed and volume do not necessarily represent how well a device will operate as a presence detector. Video detection was evaluated at two signalized intersections in West Lafayette, Indiana and Noblesville, Indiana. A camera on each approach was located at the vendor recommended position, at a height of 40 feet and offset so that the camera was approximately inline with the lane line dividing the left-turn lane and through lane. Two additional cameras were located on each approach at less optimal horizontal and vertical locations. Additionally at the West Lafayette site, a fourth camera was located directly above the stop bar so that it looked down onto the detection zone. Inductive loops were used as baseline data to screen for discrepancies. Each time the loop detectors were not in agreement with a specific video detector, a discrepancy was noted. A digital video recording was later observed to determine whether the video detector or the loop detector was in error. An analysis of the data showed video detection was found to produce statistically significantly more false detections and missed detections than the loop detectors on most phases. Generally, only very small variations in video detector performance were observed at the different camera locations. The video detection was also evaluated in terms of its’ consistency of detector turn-on and turn-off times. The video detection displays an undesirable inconsistency between night periods and day periods where it tends to activate 1 to 3 seconds earlier during the night period due to headlight reflections on the pavement. However, the camera at West Lafayette located directly above the stop bar displayed very consistent behavior between the night and day periods.

  PublisherOA PDFDOI

• Vendor Comparison of Video Detection Systems

  2006-01-01 · 14 citations

  reportOpen access1st authorCorresponding

  Video detection has become increasingly popular for presence detection at signalized intersections because of its versatility. However, several reports have documented performance problems in specific systems. This paper quantifies the performance of three different commercially available video detection systems. The systems were tested in May and September 2005 for presence detection accuracy. Prior to the May 2005 test, a representative from each vendor configured the video detection zones to match the loop detection zone as closely as possible. The outputs from the loop detection for the through-right and left-turn lane groups were compared with the corresponding output from each of the video detection systems. Whenever there was a discrepancy between the loop and video, a digital video was observed to determine the cause of the discrepancy. Missed calls and false calls were categorized for each system. The errors were also categorized according to the impact that they would have on signal operations. During a 24hr test on two separate days, the number of missed detections longer than 5 seconds ranged from 9 to 147, and the number of false calls longer than 5 seconds ranged from 16 to 149.

  PublisherOA PDFDOI

• Impact of Camera and Lighting Position on Video Detection Precision

  2006-01-01 · 1 citations

  reportOpen access1st authorCorresponding

  On well-illuminated approaches, vehicle headlight reflections on the pavement were observed to cause video detection units to activate early. This early activation results in a dramatic increase in the length of the effective vehicle detection zone. This observed variation in the effective length of the vehicle detection zone that varies by ambient lighting condition and camera placement presents a very serious impediment for traffic engineers to design vehicle extension intervals that operate correctly during day, night and transition periods. Furthermore, the stochastic variation in the length of the vehicle detection zone length has the potential to create driver expectancy issues. Tables are included that reports the observed average and range of detection zone length variations for 16 observed video cameras that were extensively calibrated by the manufacturer at the test site. The paper concludes by recommending near-side placement of video detection devices to reduce the stochastic variation in detection zone length.

  PublisherOA PDFDOI

• Evaluation of the Accuracy of Stop Bar Video Vehicle Detection at Signalized Intersections

  Transportation Research Record Journal of the Transportation Research Board · 2005-01-01 · 31 citations

  article1st authorCorresponding

  Many U.S. agencies have adopted video vehicle detection technology as an alternative to inductive loops. Although many product evaluations have been performed, the majority of these evaluations concentrated on freeway applications in which speed and volume were the primary evaluation criteria. At an actuated intersection, the metrics of speed and volume do not necessarily represent how well a device will operate as a presence detector. Video detection at signalized intersections was evaluated at a test intersection in Indiana. Cameras on all approaches were located at the optimal camera position recommended by the vendors, approximately 60 ft from the strain pole. Two additional cameras were located on each mast arm at slightly less optimal positions, 36 and 48 ft from the strain pole. Traditional inductive loops were also available at the intersection and were used to provide baseline data to screen for discrepancies. Each time the detectors were not in agreement, a discrepancy was noted. A digital video recording was later viewed by a human observer to determine whether the video detector or the loop detector was in error. An analysis of the data showed that video detection was found to produce statistically significantly more false detections and missed detections than the loop detectors on most phases. A small incremental increase in performance was observed when the camera was mounted at 60 ft rather than 36 ft on two of the approaches, but this marginal improvement likely does not justify the additional expense of mast arm, pole, and pole foundation associated with this camera location.

  PublisherDOI

• Evaluation of the Accuracy of Stop Bar Video Vehicle Detection at Signalized Intersections

  Transportation Research Record Journal of the Transportation Research Board · 2005-01-01 · 13 citations

  article1st authorCorresponding

  Many U.S. agencies have adopted video vehicle detection technology as an alternative to inductive loops. Although many product evaluations have been performed, the majority of these evaluations concentrated on freeway applications in which speed and volume were the primary evaluation criteria. At an actuated intersection, the metrics of speed and volume do not necessarily represent how well a device will operate as a presence detector. Video detection at signalized intersections was evaluated at a test intersection in Indiana. Cameras on all approaches were located at the optimal camera position recommended by the vendors, approximately 60 ft from the strain pole. Two additional cameras were located on each mast arm at slightly less optimal positions, 36 and 48 ft from the strain pole. Traditional inductive loops were also available at the intersection and were used to provide baseline data to screen for discrepancies. Each time the detectors were not in agreement, a discrepancy was noted. A digital video recording was later viewed by a human observer to determine whether the video detector or the loop detector was in error. An analysis of the data showed that video detection was found to produce statistically significantly more false detections and missed detections than the loop detectors on most phases. A small incremental increase in performance was observed when the camera was mounted at 60 ft rather than 36 ft on two of the approaches, but this marginal improvement likely does not justify the additional expense of mast arm, pole, and pole foundation associated with this camera location.

  PublisherDOI

• Comparative study of theoretical, simulation, and field platoon data

  Traffic engineering & control · 2001-01-01 · 12 citations

  articleSenior author

  Platoon dispersion along arterial links constitutes an important factor in determining whether adjacent traffic signals should be co-ordinated. The amount of dispersion also determines, to a great extent, the number of vehicular stops and total delay in the co-ordinated movements. The purpose of this study was first to evaluate the impact of distance on the dispersion of platoons discharged from intersections using data collected in the field and second to determine if similar conditions could be modelled with reasonable accuracy using the theoretical or simulation models. To evaluate the impact of distance on platoon dispersion, the proportion of platoons arriving during a series of time intervals was tabulated and plotted. These plots were used to determine the maximum percentage of the platoon that can pass through a particular green window downstream given a perfect offset. Field platoon data was compared to both Robertson's model, which is used in TRANSYT signal design software, and CORSIM simulation model. Our research found that CORSIM was more conservative in quantifying the benefit of traffic signal co-ordination for small green windows, where Robertson's model was observed to be more conservative in quantifying the benefit for large green windows as the dispersion parameter increases. (A)

  Publisher

• HIGHWAYS PAVEMENTS: USE OF TAPERED SECTIONS TO EXTEND DESIGN LIFE. DISCUSSION.

  Proceedings of the Institution of Civil Engineers - Transport · 1999-02-01

  article1st authorCorresponding

  Keywords TRANSPORT RESEARCH LABORATORY, TRL PAVEMENTS, HIGHWAYS, ROADS, SECTIONS, TAPERED, DESIGN LIFE, DESIGN, LOADS, LOADING, TRAFFIC, ECONOMICS, COSTS, THICKNESS, MATERIALS, ROADBASE... Show All

  PublisherDOI

Frequent coauthors

• F A Urquhart

  8 shared

• Darcy M. Bullock

  Purdue University West Lafayette

  5 shared

• James R. Sturdevant

  Indiana Department of Transportation

  3 shared

• David G. Candey

  Indiana Department of Transportation

  3 shared

• Jennie Middleton

  University of Oxford

  3 shared

• Zachary Clark

  2 shared

• Peter Bonsall

  University of Leeds

  1 shared

• Robert Griffin

  University of Massachusetts Dartmouth

  1 shared