Night-time Speed Research Articles

Association of Nighttime Speed Limits and Electric Scooter–Related Injuries

This cohort study investigates whether nighttime speed restrictions are associated with the incidence of electric scooter–related injuries in Finland.

Reduced speed limit is ineffective for mitigating the effects of roads on ungulates

AbstractRoads obstruct wildlife movements, and wildlife‐vehicle collisions are a hazard to both animals and humans. Wildlife and transportation managers often consider reducing the speed limit to reduce wildlife‐vehicle collisions, but there is little empirical data to support or refute this measure. We experimentally reduced the nighttime speed limit from 70 to 55 mph on six stretches of highway that cross mule deer (Odocoileus hemionus) winter range or migration paths. Drivers consistently reduced their speeds, but only by 3–5 mi/h. Reduced speed limit did not make it any easier for deer to cross the road, indicating no benefit for habitat connectivity. At winter sites, the number of deer‐vehicle collisions was not affected by the reduced speed limit whereas at migration sites, collisions were modestly lower under the reduced speed limit. Given the small reduction in vehicle speeds, it is not surprising that there was little benefit of reduced speed limit for deer or people. We conclude that reduced nighttime speed limit is not an effective way to reduce wildlife‐vehicle collisions or make roads more permeable to wildlife due to poor compliance from motorists.

Traveling ionospheric disturbances near London, Canada

Observations of medium scale traveling ionospheric disturbances (TIDs) from near London, Canada (43°N, 81°W geographic) using spaced transmitter technique at 4 MHz have been done for 1 1 2 years. Most of the best data are for daytime TIDs because of the use of 4 MHz. Using this data set we have derived properties of the TIDs such as the speed, direction of propagation and their diurnal, seasonal, and annual variations. Speeds and directions show similar diurnal variations during all months. Typical daytime speeds are of the order of 160 m/s and nighttime speeds are of the order of 300 m/s. Daytime directions are approximately eastward in morning hours and gradually rotate clockwise to approximately southward in late afternoon. Parameters of the TIDs are consistent with two possible sources: upward propagated and filtered mesospheric gravity waves, and/or the sunrise terminator.

Size, shape, orientation, speed, and duration of GPS equatorial anomaly scintillations

GPS L1 C/A signal scintillation data were collected at the equatorial anomaly over a period of three months using five receivers spaced on magnetic east‐west and north‐south axes to examine the speed, orientation, shape, width, and duration of GPS scintillation fade patterns. The nighttime speeds were primarily eastward in the range of 100–200 m/s with a significant spread to both larger values and negative (westward) values as expected, given the known behavior of ionospheric drifts and GPS signal path movement. The characteristic velocity was found to be small so that the true velocity was equal to the apparent velocity to a very good approximation. The orientation of the scintillation fade patterns was organized by a simple projection model of the magnetic field along the GPS signal path onto the horizontal plane when the signal paths were aligned no closer than 60° from the magnetic field. The shape of the scintillation fade pattern was greatly elongated in the magnetic north‐south direction, and no change could be detected over a distance of 1 km. The east‐west widths of the scintillation fade patterns were variable, but after normalizing to the elevation angle, accounting for the fade orientation, and eliminating signal paths within 60° of the magnetic field, an organized scale length of about 450 m was determined. The duration of the scintillation fade patterns was examined using the optimal cross‐correlation amplitude as a measure of change. For a 5 s duration, 49% of the optimal cross‐correlation amplitudes exceed a value of 0.8.

Headlight sight distance on separate highway alignments: a new approach

Headlight sight distance (HLSD) has been considered in the literature for only simple (isolated) sag vertical curves. This paper develops HLSD models for two-dimensional complex horizontal and vertical alignments. The horizontal alignment may consist of any combination of circular curves, spiral curves, and tangents. The HLSD model for horizontal alignment is based on the outside horizontal angles of headlight spread from the horizontal axes of the headlights. The available sight distance was modelled considering the effect of continuous (e.g., cut slope) and single obstructions. A design graph showing the adequacy of the available HLSD on simple circular curves is presented. The vertical alignment may consist of any combination of simple sag curves, simple crest curves, unsymmetrical (traditional or equal-arc) curves, and tangents. The HLSD model for vertical alignment is based on the traditional upward angle of headlight divergence from the horizontal axis of the vehicle. The model determines the available HLSD as well as headlight dips. Application of the models is illustrated using numerical examples. The presented models can be used to evaluate nighttime sight distance on complex horizontal alignments and to design sag curve as part of a complex vertical alignment, rather than as an isolated component. The HLSD models can help identify remedial measures to satisfy sight-distance needs such as advisory nighttime speeds. (A)

Wind Power as an Electrical Energy Source in Illinois

Using 3 h wind data (1970–74) from nine first-order NWS stations in and around Illinois, monthly frequency histograms of wind speeds for each station, and for each half-day (0700–1800 and 1900–0600 LST) were constructed. The histogram class interval was 2 mph. To assess the wind power for electrical power generation, the mean speed for each class was adjusted from the speed at the anemometer height to 20 m by means of a logarithmic relationship. The wind analysis showed that the maximum potential for wind-generated electricity in Illinois is found from Chicago to Springfield to north of St. Louis. Over 60% of all 3 h winds are ≥8 mph (3.6 m s−1) within that band, whereas values are <55% to the northwest and ∼40% to the southeast within Illinois. January–April are the months with the strongest winds. During winter, nighttime speeds are ∼75% of those during the day, whereas in summer they are ∼50%. Annual wind-generated electric power was calculated for each site based on the published specifications for a commercially available 1.8 kW generator and the wind climatology. From 50 to 55% of a residential electrical demand could be produced by the wind within the maximum potential area of the state, whereas only 25–30% could be wind-generated in the area with the least potential. Cost payback estimates are presented for each of the sites with various purchase and installation costs and assumed inflation rates.

Diurnal Variation of Onshore Wind Speed Near a Coastline

Abstract Surface wind data taken from 19 km offshore to 14 km inland during several days of onshore wind occurrence were reduced and analysed. The mean kinetic enemy per unit mass and its changes normal to the coastline were computed directly from the wind data. Analysis of these data shows two well defined regimes of diurnal variation in wind speed. The marine air has a nighttime speed maximum and a daytime minimum. As the air moves inland, the speed distribution becomes bimodal with the primary maximum occurring in the daytime and the secondary maximum at night. As expected Intuitively and predicted by theory, the speed changes most abruptly near the change in surface roughness (the coastline). Also as predicted by theory, complete dynamic equilibrium with the new lower boundary is not achieved until the air is ∼5–12 km downwind from the coastline.

Studies of the Horizontal Drifts in the F-Region of the Ionosphere at Ahmedabad

The paper describes the results of F-region drift measurements at Ahmedabad during different periods between 1957 and 1966, and compliments the results of E-region drifts published in an earlier paper (Rastogi 1969). During any of the season and epoch the mean drift speed is almost the same for the E or the F-region at Ahmedabad. The F-region drift speeds are found to be slightly greater during the night than during the day-time. The day-time speeds (F) are greater in winter than in summer while no consistent seasonal variation is evident for the night-time speed. The most probable direction changes from N-W to S-E direction seasonally from winter to summer or with the decrease of solar activity. The diurnal wave of E-W component for E or F-region drift are similar at Ahmedabad- Waltair or Delhi, but the diurnal wave of N-S components at Ahmedabad is opposite in phase to that in Waltair or Delhi. Ahmedabad seems to lie close to the region of transition of low and high latitude ionospheric wind system.

THREE SOUTHERLY LOW-LEVEL JET SYSTEMS DELINEATED BY THE WEATHER BUREAU SPECIAL PIBAL NETWORK OF 1961

For the first time in metcorological history the broad aspects of the southerly low-level jet o\er the Western Plains have been studied in fine detail both in time and space. This as acconiplished in the spring of 1961 by means of a line of 13 pibal stations established between Amarillo, Tex., and Little Rock, Ark. Twenty-five consecutive hourly observations were taken at each station on a total of five different 24-hr. periods in April, May, and June. Three of the observational periods were analyzed and the jet characteristics arc described. High prtssure cells east of the Great Plains, whether of polar or tropical origin, produced lo\i-le\el southerly jet systems. Jet speed maxima occurred between 300 and 800 m. above the ground (generally ~cll below the 850-nib. level) &’ CE were often found in several horizontally-arranged cells. By day the jet was incoherent (with one exception) aTld speeds were sub-geostrophic, while at night the jet was well organized and coherent and speed maxima were as high as 1.95 times the sea level geostrophic speed. The jet lifted over mountainous regions and over intruding mcsosystems. On those nights with surface inversions the speed maxima were lower in elcvation and required a smaller pressure gradient for a given maximum nighttime speed than when lapse conditions existed, but their elevation apparently had no correlation with the height of the inversion itself. Blackadar’s theory of the inertial oscillation for producing the low-level nocturnal jct is easily applicable for the practicing forecaster, but Wexler’s inertial bouildary layer interpretation predicts the jet by day as well as by night on a basic southerly current. Both theories seemed to apply at times during the existence of the jet systems described here.