How do I use a Traffic Sign Inventory?
As the owner of Mid-West GIS, as well as being in the field for over 20 years, I commonly am asked by both existing and future clients how they can and should being using our Traffic Sign Inventory GIS database. This is a very valid question, as there are many uses and functions to the data, and in order to get the most return on your investment you need to be utilizing it to its full capabilities. So I decided to share some of my questions and answers with the GIS and Traffic Sign community so that more users can take advantage of their Traffic Sign Inventory GIS data.
Question: Is the data hard to maintain?
Answer: The majority of the cost and labor is in the initial collection of the data itself. Once the data is in place, updating and maintaining the data should be very easy and really doesn’t take much time at all. Let’s take a few examples. The first would be where you have an existing sign that is already in the Traffic Sign Inventory, but has been changed out with a new sign in the field so the Traffic Sign Inventory needs to be updated. You can locate the sign one of two way; you can do a query on the database using a field such as a Sign ID, or you can simply zoom to the location of the sign in the map application if you know exactly which sign you are updating. Once you locate the sign, you select it so you can edit the database attributes. Since the sign already existed in the Traffic Sign Inventory the database attributes area already filled out with the old information. Most of this information will stay the same because you are most likely replacing with the same type of sign, for example swapping out an old stop sign with a new stop sign. Therefore, the only attributes you would need to update would be ones like Sheeting Material Type, Sign Condition, Install Date, and maybe a few others. Once you are done you save your edits and you are finished. In the second example you would be adding a new sign into the Traffic Sign Inventory that did not already exist. Let’s say you are adding a new Speed Limit 35 sign. In this instance you can also use two methods. The first is you once again zoom into the location on the map, and can add a sign point using the editing tools. Once you add the point in the correct location you would need to populate the database attributes, because they would all be blank at this point. It only takes a few minutes to go through the entire list of fields and update the information. This is similar to the process done in the field by our GIS Technicians when the initial collection is done. Once all fields are populated, and I also recommend going back over them quickly to verify the information is correct, you save your edits and are done. The other method to adding data is by using a GPS data collector in the field. This method is a little more technical but not bad if you are familiar with the GPS equipment. You would take the GPS data collector into the field, collect the point at the location the new sign has been installed, and then populate the database attributes after the point was stored. Once you are back in the office the GPS data would need to be imported back into the Traffic Sign Inventory. So, as you can see there are a few ways to both update, and maintain the data. I always recommend finding the one you are more comfortable with, and create a document that walks you through the work flow until you are familiar with all of the steps.
Question: How accurate does the GPS point need to be for a Traffic Sign Inventory?
Answer: This is a question we are asked quite often. With so many options on accuracy, it can be very confusing. It can also affect the cost of the data collection, as it is more expensive and time consuming the more accurate the GPS data is being collected. My recommendation is to go with a sub-meter accurate GPS point. The reasoning behind it is mainly because you are dealing with a feature (traffic sign) that is very visible and easy to locate in the field. You don’t have to go searching around for it once you are at the correct location where the sign is supposed to be. So, it doesn’t need to be sub-centimeter accurate like a feature such as a water valve would be. On the other had you don’t want to go with a point that is less accurate, otherwise when you are collecting a point it may end up in the middle of the street because the GPS data isn’t accurate enough. After 12 years of collecting Traffic Sign Inventories we have narrowed it down to sub-meter accuracy. Now week in mind once the GPS data has been imported into the map application, we always do a quality control check on the location using the street centerline data and the aerial photos to ensure it is in the right place. Sometimes it is off a little and we will adjust it as needed, like it may show on the sidewalk and you know its between the sidewalk and the curb, so we will move it over between the two.
Question: How do I get a list of certain types of signs for maintenance purposes?
Answer: This is the power of the GIS database, being able to query or ask a question to the database, and receive results back that you can use to make decisions. In ArcMap there is a query tool. When using this tool on the Traffic Sign Inventory data layer you can make a simple or complex query. Let’s say you wanted to get a list of Stop signs that are poor condition. When you are making the query, it lists all of the attributes out in the query builder. So, you would select “Sign type = STOP” and “Sign Condition = POOR”. It is as simple as that. When you run the query, you can open the database and all of your stop signs that are rated as poor condition should be selected. You can now print a map showing the location of the signs, as well as print the database to go with it. This is a great tool for budget planning. You can run multiple queries on the types of signs you want to replace in the upcoming budget year, then using these reports you can accurately obtain counts on how many of each sign needs to be replaced. Then you use these numbers to calculate the cost to replace each sign. Gives you the ability to present accurate numbers on what type, how many, and at what cost to the decision makers working on your budget.
Question: My computer crashed and we lost our data, how can I get it back.
Answer: Backup, Backup, Backup. Always back up your data to another source. Too much time, effort, and money are put into the creation and maintenance of this type of data to take chances losing it. I always tell my clients to keep a backup of the data off-site. Now that there is an amazing amount of cloud storage for a reasonable cost this is the route I recommend. Most Traffic Sign Inventories are not to large to use this storage option. On average I would say they are between 30 and 50 megabytes. Now that does not include digital photos if you have that as an attribute. Those can be quite large. So, in the end, find an external backup option that works best for you and make sure you utilize it on a regular basis. I try to make nightly backups of critical data, and weekly backups of the rest. Seems like overkill, until you lose a hard drive and need that data back.
These are a few of the more common questions. I plan on doing a second installment of this article soon and sharing others that we receive as well. It is always good to share knowledge with each other. We learn from each other’s successes as well as our failures.