Data collection of road traffic is very important and essential for traffic engineers in order to help achieving a safe and efficient travel journey in urban and rural environments. Many developing countries suffer from the lack of sufficient, reliable and continuous road traffic data. Therefore, traffic engineers in these countries usually rely on short-term traffic counts and estimations. In many cases, they use other countries traffic expansion factors in their design calculations and they generally do so without prior local verifications. Almasri, Sarraj and Eljamassi indicated that developing cities face several challenges in their planning efforts and development of transportation facilities. One of these challenges is the lack or absence of transportation data such as traffic flow, vehicular speed and delay that are used to evaluate the current traffic situation [1]. It is, therefore, very important to work on providing more road traffic data. These data should be reliable, accurate and as comprehensive as possible.

This research tries to provide information based on scarcely available local road traffic counts. The main objective is to generate an accessible reference that provides hourly and daily traffic expansion factors on three selected main roads in Gaza city, for the benefit of traffic engineers, experts, researchers as well as students.

Traffic flow usually varies from hour to hour, from day to day and from season to season. This characteristic of traffic flow implies that traffic engineers should deal carefully and wisely with traffic flow information. It is simply not acceptable to estimate the traffic flow on one day (24 hours) by counting flow in one hour of that day and multiplying its value with 24. The hour-to-hour variation of traffic flow creates peak periods and hence it is very essential to determine the morning and evening peaks for the purpose of design among other important purposes. Nicholas Garber and Lester Hoel in their respected and well-known book; Traffic and Highways Engineering, illustrated that “Although traffic volume at a section of a road varies from time to time, this variation is repetitive and rhythmic” [2]. They also indicated that these characteristics of traffic volume are very useful when traffic counts are being planned. This also means that traffic volumes collected at different times or places can be related to each other and knowledge of these characteristics of traffic flow can be used to estimate the accuracy of traffic counts.

Bonsall and O'Flaherty [3] stated, “information on the flow of vehicles past a given point in a specified time period provides a key input to decisions on the planning, design and operation of transport systems.” They also mentioned that “if data are collected at a site on a continuous basis for a year or more, then quantities can be calculated precisely in arrears, but if the count is of limited duration, it becomes necessary to make estimates based on what is known about seasonal flow patterns at other sites.” In many cases, it is important to estimate the annual average daily (AADT), the average daily traffic (ADT), the peak hour period and the peak hour flow for a specific site. Leduc considers the AADT as a crucial raw traffic data for countless of applications and its estimation methodology is typically based on both continuous and temporary traffic counts that are afterwards used as inputs to sophisticated mathematical models [4].

In the UK, the Traffic Appraisal Manual [5] indicates that a short period count can be used to provide estimates of traffic flows of sufficient accuracy for some purposes. It gives an example that a 4-hour count of vehicles might be used to estimate the annual flow with a coefficient of variation of about 10% for an urban road. It also suggests that a short period count be factored up to 16 hours, and then the 16-hour estimate to be factored up to AADT.

The Department for Transport in the UK devised expansion factors for estimating AADT from short period counts at various times of year. It should be noted that the expansion factors are different for different types of road [3]. According to that, AADT can be estimated from very short counts such as 2-hour counts. However, longer counts are expected to give a better estimate and traffic flow estimates derived from short period counts should be treated with considerable caution. This is due to the changeable characteristic of traffic flows, because it might be distorted by public holidays and changes in weather conditions.

The Traffic Appraisal Manual indicated in 1997 that the use of national (rather than local) expansion factors for converting short period counts to AADT and other periods is now no longer recommended. Local Automatic Traffic Count data should be used instead [6].

Garber and Hoel [2] stated: it is common that in less developed cities, traffic flow counts of durations shorter than 24 hours are required in many situations to be expanded to 24-hour volumes. This is also necessary when estimations of the ADT or AADT are needed quickly or when the available budget is very limited. In order to work out such expansion of traffic counts, hourly expansion factors are used. These factors can be determined using data obtained at continuous count stations. Hourly expansion factors (HEFs) are determined by the formula [2]:

The HEFs are used to expand traffic counts of durations shorter than 24 hours to 24-hour volumes by multiplying the hourly volume for each hour during the short count period by the HEF for that hour and finding the mean of these products.

It is also possible to expand traffic volumes collected on a particular day of the week in order to get estimates of the average flow per day in that week. For this purpose, Daily Expansion Factors (DEFs) are computed. DEF is determined by the formula [2]:

The DEFs are used to determine the total traffic volume per week from counts of 24-hour duration by multiplying the 24-hour volume by the DEF. The result is then divided by 7 in order to determine an estimate of the average flow per day (ADT) in that week.

Moreover, estimates of the Average Annual Daily Traffic (AADT) can be computed using Monthly Expansion Factors (MEFs), which are computed as [2]:

Therefore, given the ADT value for a particular month in a given year; the AADT for this year may be obtained by multiplying this ADT by the MEF.

The above expansion factors should be determined for each class of road in the classification system established for an area. Major roads may be classified as freeways, expressways, and major arterials. However, minor roads may be classified as residential, commercial, and industrial streets. Each class should consist of highway links with similar traffic patterns and characteristics. A highway link is defined for traffic count purposes as a homogeneous section that has the same characteristics, such as AADT, and daily, weekly, and seasonal variations in traffic volumes at each point [2].

The city of Gaza is located in the Gaza Strip that lies on the eastern coast of the Mediterranean Sea. Gaza is the biggest city in Gaza Strip with a total area of about 56km² and a total population of more than 625 thousand. The total length of roads is more than 900km where less than 38% of which is paved [7]. The total number of registered vehicles in the city is estimated at about 40,000 out of 70,531; the total number of registered vehicles in Gaza Strip by the end of 2017.

Traffic data collection in Gaza Strip is currently suffering from several difficulties and hitches. The most important one is the lack of a formal or official body that is responsible for organizing and achieving this task. Bashbash and Sarraj [8] said that “The available traffic statistics in Gaza city are chaotic and without good management.” After the Israeli occupation of Gaza Strip in 1967, limited traffic flow surveys used to be conducted by the Occupation Authorities. Some results of these surveys used to be published quarterly between 1970 and 1994. After the establishment of the Palestinian National Authority (PNA) in 1994, some efforts were exerted by the Ministry of Planning and International Cooperation (MOPIC). They started by continuing publishing the quarterly Statistical Bulletin which used to be published before. One example of such publications was issued in November 1995. This particular bulletin contained data on several subjects including transportation. The information on transportation included statistics on the following topics:

• Drivers and vehicles registered in Gaza Strip by type of vehicle.
• Road accidents by casualty severity of accidents.
• Traffic flow counts on selected roads in Gaza Strip.

The traffic flow counts were conducted on 32 locations across Gaza Strip, about 44% of these locations were in Gaza city. The traffic counts were classified by vehicle type and were conducted for duration of 12 hours at each location [9]. In 1996, a traffic survey was also conducted by MOPIC in cooperation with the Civil Engineering Department at the Islamic University of Gaza. This survey involved collection of traffic flow counts at 16 main road intersections on Salah El-Deen Road in Gaza Strip; the main arterial road that connects BeitHanoun in the north with Rafah in the south. Traffic flow was counted for a period of 12 hours for one day [10].

Other studies were also carried out on traffic flow and published some reports that included limited traffic statistics. Two of these publications were released by NATUF for Environment and Development, which is a local NGO. NATUF published a report that summarizes traffic data collected at 5 main road intersections in Gaza city [11] and another report that describes a detailed traffic study on the city of Rafah [12]. In 2007, Yahya Sarraj prepared a report that collected and analysed several traffic surveys conducted in Gaza Strip between 1994 and 2006 [13]. In 2010, the Ministry of Planning released a report on the sectorial planning of roads and transportation, which included data on traffic flow and other traffic-related useful information [14]. However, none of the mentioned studies provided any estimation of hourly, daily or monthly expansion factors and most traffic surveys were made for periods less than 24 hours.

The findings of this paper are based on recently collected continuous traffic flow counts on three main roads in Gaza city. The traffic counts were part of the graduation project of three civil engineering students; supervised by Dr Yahya Sarraj [15]. The project involved the collection of classified traffic flow counts for 24 hours on seven consecutive days at three different locations. The traffic flow counts were carried out between February 10^thand March 15^th2016. Data were collected using a digital video camera and the recordings were manually analysed at the office.

4.1. Location of Counts

Continuous traffic flow counts were conducted for a period of a week on each of the selected three main roads in Gaza city; AlJala'a, AlNassr and AlWehda Streets. The locations of traffic flow counts are shown in Fig. (1).

Fig. (1). The location of traffic flow counting stations on three main roads in gaza, palestine (source: Land authority, Palestine, with modifications).

The results of this research indicate that the average HEFs obtained on the three studied main streets in Gaza city can be used with 95% confidence. The analysis proved that the average HEFs in the period between 7:00 and 16:00 are the most appropriate. This is because the margin of error in this period is less than ±3%. In order to get the best accuracy, the results recommend applying these factors on traffic counts obtained on weekdays rather than weekends. The results also recommend that the average values of the HEFs of the three streets may be applied on other main streets of Gaza in order to obtain estimates of the ADT.

The results indicate that the DEFs obtained by this work can be used to estimate the ADT with a maximum margin of error of about 10%. However, Sunday and Monday are probably the best weekdays to get the most accurate estimation of ADT. This is because they have the lowest margin of error among weekdays (1.9% to 3.2%) and they are more likely to represent an average day of the week.

A maximum PHV of 2864 vehicles/hour was recorded on Al Jalaa Street on Wednesday between 7:00 and 8:00 in the morning. The average peak-to-daily ratio (p/d) of the three streets was found to be 7.18%. On the other hand, the maximum directional traffic split (D) was found to be 60% in the heaviest direction of traffic flow during the peak period.