How do you calm a nervous dog?

Agree with the previous answers and definitely suggest carrying treats with you. The biggest thing is training the "Look" command or "Attention" command or whatever you want to call it. If you train that inside first, sometimes you can get the dog's attention on the treat and then give them the treat if they remain calm. If they lose it because the skate boarder got too close, then I just walk the other way and they don't get the treat. As has been noted, it takes a long time for this to change the behavior permanently, but usually it does help at least a little in the short term.

If I encounter a potentially frightening situation while out on a dog walk, I usually just turn and walk the opposite direction. This includes other dogs, loud garbage trucks, motorcycles, etcetera. I don't usually attempt to do any positive reinforcement training with these situations. Usually adult dogs are more "stuck in their ways" and as the dog sitter, I am not the primary caregiver. I only see the average Rover dog every other month or so, even once a year for some. Not enough time to do any meaningful training. However, if it's a puppy I always offer some training in these situations. We sit down on the sidewalk where they are scared of the garbage truck/construction, and I give treats for positive reactions (curiosity, looking at the object, moving towards the object, tail up).

I find that taking a deep breath myself, keeping a calm demeanor and getting my body between what is frightening him works, when done consistently. Just keep walking, calmly. I would give a treat and praise him immediately AFTER he has passed his apprehensive situation. Giving him praise and a treat prior or during the uncomfortable period, only reinforces his actions. He's getting the message that as long as I stay nervous, I'll get a reward. I think the previous comments get the idea.

I would also take a look at other opportunities to develop the relationship outside of the situation. Is trust and training effective at other times? If walking through a stressful area is the only issue, introducing those areas over a period of time with trust and leadership can be effective. Other non-stressful area can provide a good exercise time. The key is understanding the queues we give and that of our fury friends and enforcing a trusting bond. My first step is to identify the breed and mix, then read breed literature to reinforce my understanding, then develop the relationship progressively over time. Happy trails.

I make sure I protect the dog from the noise by blocking his sight from the noise, ie kid screaming, lawnmower, motorcycle...telling him that it is ok, and once he gets past it or as he's moving past it, reassure him that he's ok and a good boy.....repeating its ok and good boy. Every time he does that and I pet him and make eye contact with reassurance.